JP5342657B2 - Display device - Google Patents

Abstract

A display device which can prevent deterioration of a liquid crystal and reduction in display quality at low power consumption without lowering an aperture ratio is provided. An opposite voltage (Vcom) is applied to an opposite electrode (80) of a liquid crystal capacitive element (Clc). One ends of a pixel electrode (20), a first switch circuit (22), a second switch circuit (23), and a first terminal of a second transistor (T2) form an internal node (N1). The other ends of the first switch circuit (22) and the second switch circuit (23) are connected to a source line (SL) and a voltage supply line (VSL), respectively. A control terminal of a first transistor (T1) in the second switch circuit (23), a second terminal of the second transistor (T2), and one end of a boost capacitive element (Cbst) form an output node (N2). The other end of the boost capacitive element (Cbst) and the control terminal of the second transistor (T2) are connected to a boost line (BST) and a reference line (REF), respectively. This configuration makes it possible to perform an action (self-refresh action) to return the absolute value of the voltage between both ends of a display element part to the value at the time of a last writing action without performing a writing action.

Description

  The present invention relates to a pixel circuit and a display device including the pixel circuit, and more particularly to an active matrix display device.

  A portable terminal such as a mobile phone or a portable game machine generally uses a liquid crystal display device as its display means. In addition, since mobile phones and the like are driven by a battery, reduction of power consumption is strongly demanded. For this reason, information that always needs to be displayed, such as time and remaining battery power, is displayed on the reflective sub-panel. In recent years, it has been demanded that both the normal display by the full color display and the continuous display by the reflection type are compatible on the same main panel.

  FIG. 47 shows an equivalent circuit of a pixel circuit of a general active matrix liquid crystal display device. FIG. 48 shows a circuit arrangement example of an active matrix liquid crystal display device with m × n pixels. Note that m and n are both integers of 2 or more.

  As shown in FIG. 48, a switching element made of a thin film transistor (TFT) is provided at each intersection of m source lines SL1, SL2,..., SLm and n scanning lines GL1, GL2,. . In FIG. 47, each source line SL1, SL2,..., SLm is represented by the source line SL, and similarly, each scanning line GL1, GL2,. .

  As shown in FIG. 47, the liquid crystal capacitive element Clc and the auxiliary capacitive element Cs are connected in parallel via the TFT. The liquid crystal capacitive element Clc has a laminated structure in which a liquid crystal layer is provided between the pixel electrode 20 and the counter electrode 80. The counter electrode is also called a common electrode.

  In FIG. 48, for each pixel circuit, only the TFT and the pixel electrode (black rectangular portion) are simply displayed.

  The auxiliary capacitor Cs has one end (one electrode) connected to the pixel electrode 20 and the other end (the other electrode) connected to the auxiliary capacitor line CSL, and stabilizes the voltage of the pixel data held in the pixel electrode 20. . The auxiliary capacitor Cs has the following characteristics: the capacitance of the liquid crystal capacitor Clc varies between black display and white display due to the leakage current of the TFT and the dielectric anisotropy of the liquid crystal molecules, and the parasitic capacitance between the pixel electrode and the peripheral wiring. This has the effect of suppressing the fluctuation of the voltage of the pixel data held in the pixel electrode due to the voltage fluctuation or the like generated through the pixel electrode. By sequentially controlling the scanning line voltage, the TFT connected to one scanning line becomes conductive, and the voltage of pixel data supplied to each source line is written to the corresponding pixel electrode in units of scanning lines.

  In normal display by full color display, even when the display content is a still image, the same display content is repeatedly written to the same pixel for each frame. Thus, by updating the voltage of the pixel data held in the pixel electrode, voltage fluctuation of the pixel data is suppressed to the minimum, and display of a high-quality still image is ensured.

  The power consumption for driving the liquid crystal display device is almost governed by the power consumption for driving the source line by the source driver, and is generally expressed by the following relational expression (1). In Equation 1, P is power consumption, f is refresh rate (number of refresh operations for one frame per unit time), C is load capacity driven by the source driver, V is drive voltage of the source driver, and n is The number of scanning lines, m indicates the number of source lines. Here, the refresh operation refers to an operation of applying a voltage to the pixel electrode through the source line while maintaining display contents.

(Equation 1)
P∝f ・ C ・ V ²・ n ・ m

  By the way, in the case of the constant display, since the display content is a still image, it is not always necessary to update the voltage of the pixel data for each frame. For this reason, in order to further reduce the power consumption of the liquid crystal display device, the refresh frequency during the constant display is lowered. However, when the refresh frequency is lowered, the pixel data voltage held in the pixel electrode varies due to the leakage current of the TFT. The voltage fluctuation becomes a fluctuation in display brightness (liquid crystal transmittance) of each pixel and is observed as flicker. In addition, since the average potential in each frame period also decreases, there is a possibility that display quality may be deteriorated such that sufficient contrast cannot be obtained.

  Here, in the continuous display of still images such as the remaining battery level and time display, as a method for simultaneously solving the problem that the display quality deteriorates due to the decrease in the refresh frequency and the reduction in power consumption, for example, Patent Document 1 below. Is disclosed. In the configuration disclosed in Patent Document 1, liquid crystal display with both transmissive and reflective functions is possible, and a pixel circuit in a pixel region capable of reflective liquid crystal display has a memory unit. . This memory unit holds information to be displayed on the reflective liquid crystal display unit as a voltage signal. At the time of reflection type liquid crystal display, the pixel circuit reads out the voltage held in the memory portion, thereby displaying information corresponding to the voltage.

  In Patent Document 1, the memory unit is configured by an SRAM, and the voltage signal is statically held. Therefore, a refresh operation is not necessary, and display quality can be maintained and power consumption can be reduced at the same time.

JP 2007-334224 A

  However, in the liquid crystal display device used in a mobile phone or the like, in the case of adopting the above configuration, in addition to the auxiliary capacitance element for holding the voltage of each pixel data as analog information during normal operation, It is necessary to provide a memory unit for storing pixel data for each pixel or each pixel group. As a result, the number of elements and the number of signal lines to be formed on the array substrate (active matrix substrate) constituting the display unit in the liquid crystal display device increases, and the aperture ratio in the transmission mode decreases. Further, when a polarity inversion driving circuit for alternating current driving of the liquid crystal is provided together with the memory unit, the aperture ratio is further reduced. As described above, when the aperture ratio decreases due to the increase in the number of elements and the number of signal lines, the luminance of the display image in the normal display mode decreases.

  On the other hand, when the memory portion as described above is not provided, in FIG. 47, a leak current is generated between the pixel electrode 20 and the source line SL via the TFT, and the potential of the pixel electrode 20 varies as described above. And appear as flicker.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a display device capable of preventing deterioration of liquid crystal and display quality with low power consumption without causing a decrease in aperture ratio. is there.

In order to achieve the above object, a display device according to the present invention is a display device having a pixel circuit group in which a plurality of pixel circuits are arranged,
The pixel circuit includes:
A display element unit including a unit display element;
An internal node that forms part of the display element unit and holds a voltage of pixel data applied to the display element unit;
A first switch circuit for transferring a voltage of the pixel data supplied from a data signal line to the internal node via at least a predetermined switch element;
A second switch circuit for transferring a voltage supplied to a predetermined voltage supply line to the internal node without passing through the predetermined switch element;
A control circuit for holding a predetermined voltage corresponding to the voltage of the pixel data held by the internal node at one end of the first capacitor element and controlling conduction / non-conduction of the second switch circuit,
Of the first and second transistor elements having a first terminal, a second terminal, and a control terminal for controlling conduction between the first and second terminals, the second switch circuit includes the first transistor element. Each of the control circuits has the second transistor element,
The control circuit includes a series circuit of the second transistor element and the first capacitor element,
One end of the first switch circuit is connected to the data signal line,
One end of the second switch circuit is connected to the voltage supply line,
The other ends of the first and second switch circuits and the first terminal of the second transistor element are connected to the internal node,
A control terminal of the first transistor element, a second terminal of the second transistor element, and one end of the first capacitor element are connected to each other to form an output node of the control circuit;
A control terminal of the second transistor element is connected to the first control line;
The other end of the first capacitive element is connected to a second control line;
The predetermined switch element is a third transistor element having a first terminal, a second terminal, and a control terminal for controlling conduction between the first and second terminals, and the control terminal is connected to a scanning signal line. Is a configuration to
A data signal line driving circuit for driving the data signal line separately, a control line driving circuit for driving the first control line, the second control line, and the voltage supply line separately, and scanning for driving the scanning signal line It has a signal line drive circuit,
For a plurality of the pixel circuits, the data signal line drive circuit, the control line drive circuit, during a self-refresh operation that operates the second switch circuit and the control circuit to simultaneously compensate for voltage fluctuations of the internal node, And the scanning signal line driving circuit is configured to control the operation according to a predetermined sequence,
The predetermined sequence is:
The scanning signal line driving circuit applies a first scanning voltage to the scanning signal lines connected to all the pixel circuits included in the pixel circuit group, thereby bringing the third transistor element into a non-conductive state. When,
When the voltage state of the binary pixel data held by the internal node is the first voltage state with respect to the first control line, the control line driving circuit causes the first capacitor element to be driven by the second transistor element. A second step of applying a first control voltage that cuts off a current from one end of the transistor to the internal node and makes the second transistor element conductive when in a second voltage state;
After execution of the first and second steps, the control line driving circuit applies the first boost voltage to the second control line, whereby the first capacitive element is connected to one end of the first capacitive element. When the voltage of the internal node is in the first voltage state, the first transistor element is turned on without being suppressed when the voltage of the internal node is in the first voltage state. A third step of bringing the first transistor element into a non-conducting state when the voltage is in the second voltage state;
After the third step, the control line driving circuit changes the voltage applied to the first control line to the second control voltage, so that the voltage state of the internal node is the first voltage state or the second voltage. A fourth step of interrupting a current from one end of the first capacitive element toward the internal node by the second transistor element regardless of a state;
After the fourth step, the scanning signal line driving circuit applies a second scanning voltage to the scanning signal lines connected to all of the pixel circuits included in the pixel circuit group to thereby apply the third transistor element. And the data line drive control circuit applies a voltage of the pixel data in the second voltage state to the data signal line;
After the fifth step, the scanning signal line driving circuit applies the first scanning voltage to the scanning signal lines connected to all the pixel circuits included in the pixel circuit group to thereby apply the third transistor. The element is turned off, and the control line driving circuit applies the voltage of the pixel data in the first voltage state to all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. And a sixth step.

In addition to the above features, the display device of the present invention is configured such that the second switch circuit is a series circuit of a fourth transistor element having a control terminal connected to a third control line and the first transistor element,
The control line driving circuit is configured to drive the third control line in addition to the first and second control lines,
The sixth step of the predetermined sequence includes:
All of the control line driving circuits connected to the plurality of pixel circuits to be subjected to the self-refresh operation in a state where the fourth transistor element is turned on by applying a predetermined voltage to the third control line. Another feature is that the pixel data voltage in the first voltage state is applied to the voltage supply line.

In addition to the above characteristics, the display device of the present invention is configured such that the data signal line is also used as the voltage supply line,
The sixth step of the predetermined sequence includes:
Instead of the control line driving circuit, the data line driving circuit applies the first voltage to the data signal lines that also serve as all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. Another feature is that the operation is to apply a voltage of the pixel data in a state.

In addition to the above features, the display device of the present invention further includes a second capacitor element having one end connected to the internal node and the other end connected to the fourth control line.
The fourth control line is also configured as the voltage supply line,
In the predetermined sequence, the first voltage state is applied to all the fourth control lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation by the control line driving circuit over the first to sixth steps. Another feature is that the voltage of the pixel data is applied.

In the present invention, in addition to the above feature, in the pixel circuit, the first switch circuit is a series circuit of the fourth transistor element and the third transistor element in the second switch circuit, or the second switch. A fifth transistor having a control terminal connected to a control terminal of the fourth transistor element in the circuit and a third circuit element of the third transistor element;
The predetermined sequence has an operation in which at least in the fifth step and the sixth step, the control line driving circuit applies a predetermined voltage to the third control line to make the fourth transistor element conductive. Another feature.

  According to the present invention, in addition to the above feature, the second switch circuit is configured by a series circuit of a fourth transistor element having a control terminal connected to the second control line and the first transistor element. Another feature.

In addition to the above features, the present invention is a configuration in which the data signal line is also used as the voltage supply line,
The sixth step in the predetermined sequence includes:
Instead of the control line driving circuit, the data line driving circuit applies the first voltage to the data signal lines that also serve as all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. Another feature is that the operation is to apply a voltage of the pixel data in a state.

In the present invention, in addition to the above feature, in the pixel circuit, the first switch circuit is a series circuit of the fourth transistor element and the third transistor element in the second switch circuit, or the second switch. Another feature is that the circuit is configured by a series circuit of a fifth transistor and a third transistor element having a control terminal connected to a control terminal of the fourth transistor element in the circuit.

In the present invention, in addition to the above feature, the predetermined sequence includes:
After the sixth step, the control line driving circuit changes the voltage applied to the first control line to a third control voltage, so that the voltage state of the internal node is the first voltage state or the second voltage. Another feature is that a seventh step of conducting the second transistor element regardless of the state to bring the internal node and the output node to the same potential is provided.

  According to the configuration of the present invention, it is possible to execute an operation (self-refresh operation) for restoring the absolute value of the voltage across the display element unit to the value at the time of the immediately preceding write operation without using the write operation. In particular, according to the present invention, instead of performing separate control for each pixel circuit, the same control is performed on the signal lines connected to all the pixel circuits to be self-refreshed, so that The pixel circuit written in the voltage state is refreshed to the first voltage state, and the pixel circuit written in the second voltage state is refreshed to the second voltage state. Accordingly, complicated control is not required, and the number of signal line driving operations can be greatly reduced as compared with the case where refresh is performed by performing a normal write operation, and low power consumption can be realized.

The block diagram which shows an example of schematic structure of the display apparatus of this invention Partial cross-sectional schematic structure diagram of a liquid crystal display device The block diagram which shows an example of schematic structure of the display apparatus of this invention The circuit diagram which shows the basic circuit structure of the pixel circuit of this invention The circuit diagram which shows the other basic circuit structure of the pixel circuit of this invention The circuit diagram which shows the other basic circuit structure of the pixel circuit of this invention Group W pixel circuit Group X first type pixel circuit Another pixel circuit of the first type of group X Another pixel circuit of the first type of group X Group X second type pixel circuit Group X type 3 pixel circuit Group X type 4 pixel circuit Another pixel circuit of Group X type 4 Another pixel circuit of Group X type 4 Another pixel circuit of Group X type 4 Group X type 5 pixel circuit Another pixel circuit of Group X type 5 Another pixel circuit of Group X type 5 Group Y first type pixel circuit Group Y second type pixel circuit Group Y type 4 pixel circuit Group Y type 5 pixel circuit Example of timing diagram of self-refresh operation by group W pixel circuits Another example of timing chart of self-refresh operation by pixel circuits of group W Example of timing chart of self-refresh operation by first type pixel circuit of group X Another example of timing chart of self-refresh operation by first type pixel circuit of group X Another example of timing chart of self-refresh operation by first type pixel circuit of group X Example of timing diagram of self-refresh operation by second type pixel circuit of group X Another example of timing chart of self-refresh operation by group X second type pixel circuit Example of timing diagram of self-refresh operation by group X type 3 pixel circuit Example of timing diagram of self-refresh operation by group X type 4 pixel circuit Example of timing diagram of self-refresh operation by group X type 5 pixel circuit Timing chart of self-refresh operation by first-type and fourth-type pixel circuits of group Y Timing chart of self-refresh operation by group Y type 2 and type 5 pixel circuits Another example of timing chart of self-refresh operation by pixel circuit of group W Pixel circuit of another embodiment of group X Pixel circuit of another embodiment of group Y Pixel circuit of another embodiment of group Y Timing chart of writing operation in the constant display mode by the pixel circuit of group W Timing chart of writing operation in the always-on display mode by the first type pixel circuit of group X Timing chart of write operation in the always-on display mode by the group X type 4 pixel circuit Flow chart showing execution procedure of write operation and self-refresh operation in the constant display mode Timing diagram of write operation in normal display mode by pixel circuit of group W The circuit diagram which shows another basic circuit structure of the pixel circuit of this invention The circuit diagram which shows another basic circuit structure of the pixel circuit of this invention Equivalent circuit diagram of pixel circuit of general active matrix type liquid crystal display device Block diagram showing a circuit arrangement example of an active matrix liquid crystal display device with m × n pixels

  Embodiments of a pixel circuit and a display device of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected about the component same as FIG.47 and FIG.48.

[First Embodiment]
In the first embodiment, a configuration of a display device of the present invention (hereinafter simply referred to as “display device”) and a pixel circuit included therein will be described.

<Display device>
FIG. 1 shows a schematic configuration of the display device 1. The display device 1 includes an active matrix substrate 10, a counter electrode 80, a display control circuit 11, a counter electrode drive circuit 12, a source driver 13, a gate driver 14, and various signal lines to be described later. On the active matrix substrate 10, a plurality of pixel circuits 2 are arranged in the row and column directions to form a pixel circuit array.

  In FIG. 1, the pixel circuit 2 is displayed in blocks in order to avoid the drawing from becoming complicated. In order to clarify that various signal lines are formed on the active matrix substrate 10, the active matrix substrate 10 is illustrated on the upper side of the counter electrode 80 for convenience.

  In the present embodiment, the display device 1 is configured to perform screen display in the two display modes of the normal display mode and the constant display mode using the same pixel circuit 2. The normal display mode is a display mode in which a moving image or a still image is displayed in a full color display, and a transmissive liquid crystal display using a backlight is used. On the other hand, in the constant display mode of this embodiment, two gradations (monochrome) are displayed in units of pixel circuits, and three adjacent pixel circuits 2 are assigned to each of the three primary colors (R, G, B), and eight colors are displayed. The display mode to display. Further, in the constant display mode, it is also possible to increase the number of display colors by area gradation by combining a plurality of adjacent three pixel circuits. Note that the constant display mode of the present embodiment is a technique that can be used for both transmissive liquid crystal display and reflective liquid crystal display.

  In the following description, for the sake of convenience, the minimum display unit corresponding to one pixel circuit 2 is referred to as “pixel”, and “pixel data” written to each pixel circuit is displayed in color by three primary colors (R, G, B). In this case, gradation data for each color is obtained. In the case of color display including black and white luminance data in addition to the three primary colors, the luminance data is also included in the pixel data.

  FIG. 2 is a schematic cross-sectional structure diagram showing the relationship between the active matrix substrate 10 and the counter electrode 80, and shows the structure of the display element unit 21 (see FIG. 4) that is a component of the pixel circuit 2. The active matrix substrate 10 is a light transmissive transparent substrate, and is made of, for example, glass or plastic.

  As shown in FIG. 1, the pixel circuit 2 including each signal line is formed on the active matrix substrate 10. In FIG. 2, the pixel electrode 20 is illustrated as a representative of the components of the pixel circuit 2. The pixel electrode 20 is made of a light transmissive transparent conductive material, for example, ITO (indium tin oxide).

  A light transmissive counter substrate 81 is disposed so as to oppose the active matrix substrate 10, and a liquid crystal layer 75 is held in a gap between the two substrates. Polarizing plates (not shown) are attached to the outer surfaces of both substrates.

  The liquid crystal layer 75 is sealed with a sealing material 74 at the peripheral portions of both substrates. On the counter substrate 81, a counter electrode 80 made of a light transmissive transparent conductive material such as ITO is formed so as to face the pixel electrode 20. The counter electrode 80 is formed as a single film so as to spread over the counter substrate 81 substantially on one surface. Here, a unit liquid crystal display element Clc (see FIG. 4) is formed by one pixel electrode 20, the counter electrode 80, and the liquid crystal layer 75 sandwiched therebetween.

  Further, a backlight device (not shown) is disposed on the back side of the active matrix substrate 10, and can emit light in a direction from the active matrix substrate 10 toward the counter substrate 81.

  As shown in FIG. 1, a plurality of signal lines are formed in the vertical and horizontal directions on the active matrix substrate 10. Then, m source lines (SL1, SL2,..., SLm) extending in the vertical direction (column direction) and n gate lines (GL1, GL2,..., SL extending in the horizontal direction (row direction). A plurality of pixel circuits 2 are formed in a matrix at a location where GLn) intersects. m and n are both natural numbers of 2 or more. Each source line is represented by “source line SL”, and each gate line is represented by “gate line GL”.

  Here, the source line SL corresponds to a “data signal line”, and the gate line GL corresponds to a “scanning signal line”. The source driver 13 corresponds to a “data signal line driving circuit”, the gate driver 14 corresponds to a “scanning signal line driving circuit”, and the counter electrode driving circuit 12 corresponds to a “counter electrode voltage supply circuit”. A part of the control circuit 11 corresponds to a “control line driving circuit”.

  In FIG. 1, the display control circuit 11 and the counter electrode drive circuit 12 are illustrated so as to exist separately from the source driver 13 and the gate driver 14, respectively, but the display control circuit is included in these drivers. 11 and the counter electrode drive circuit 12 may be included.

  The configuration shown in FIG. 1 includes a reference line REF, an auxiliary capacitance line CSL, a voltage supply line VSL, and a boost line BST as signal lines for driving the pixel circuit 2 in addition to the source line SL and the gate line GL. . In another configuration (FIG. 3), a selection line SEL is further provided.

  The voltage supply line VSL can be an independent signal line as shown in FIG. 1, or can be shared with the source line SL and the auxiliary capacitance line CSL. By sharing the voltage supply line VSL with other signal lines, the number of signal lines to be arranged on the active matrix substrate 10 can be reduced, and the aperture ratio of each pixel can be improved.

  The reference line REF, boost line BST, and selection line SEL correspond to “first control line”, “second control line”, and “third control line”, respectively, and are driven by the display control circuit 11. The auxiliary capacitance line CSL corresponds to the “fourth control line” and is driven by the display control circuit 11 as an example.

  In FIG. 1, the voltage supply line VSL, the reference line REF, the boost line BST, and the auxiliary capacitance line CSL are provided in each row so that all of the selection lines SEL extend in the row direction. The wiring of each row is connected to each other at the peripheral part of the pixel circuit array, but the wiring of each row is individually driven, and a common voltage can be applied according to the operation mode. May be. Further, depending on the type of circuit configuration of the pixel circuit 2 described later, a part or all of the reference line REF, the auxiliary capacitance line CSL, and the selection line SEL can be provided in each column so as to extend in the column direction. Basically, the reference line REF, the boost line BST, and the auxiliary capacitance line CSL are configured to be used in common by the plurality of pixel circuits 2. Further, the selection line SEL is also used in common by the plurality of pixel circuits 2 when it is provided.

  The display control circuit 11 is a circuit that controls each writing operation in a normal display mode and a constant display mode, which will be described later, and a self-refresh operation in the constant display mode.

  During the writing operation, the display control circuit 11 receives the data signal Dv representing the image to be displayed and the timing signal Ct from the external signal source, and based on the signals Dv and Ct, the image is displayed on the display element unit 21 ( As the signals to be displayed in FIG. 4), the digital image signal DA and the data side timing control signal Stc given to the source driver 13, the scanning side timing control signal Gtc given to the gate driver 14, and the counter electrode drive circuit 12 are given. The counter voltage control signal Sec and each signal voltage applied to the reference line REF, the auxiliary capacitance line CSL, the boost line BST, the voltage supply line VSL, and the selection line SEL (if provided) are generated.

  The source driver 13 is a circuit that applies a source signal having a predetermined voltage amplitude to each source line SL at a predetermined timing during a write operation and a self-refresh operation under the control of the display control circuit 11.

  During the writing operation, the source driver 13 applies a voltage that corresponds to the voltage level of the counter voltage Vcom corresponding to the pixel value for one display line represented by the digital signal DA based on the digital image signal DA and the data side timing control signal Stc. Source signals Sc1, Sc2,..., Scm are generated every horizontal period (also referred to as “1H period”). The voltage is a multi-gradation analog voltage in the normal display mode, and a two-gradation (binary) voltage in the constant display mode. Then, these source signals are applied to the corresponding source lines SL1, SL2,.

  In the self-refresh operation, the source driver 13 applies the same voltage at the same timing to all the source lines SL connected to the target pixel circuit 2 under the control of the display control circuit 11 ( Details will be described later).

  The gate driver 14 is a circuit that applies a gate signal having a predetermined voltage amplitude to each gate line GL at a predetermined timing during a write operation and a self-refresh operation under the control of the display control circuit 11. The gate driver 14 may be formed on the active matrix substrate 10 as in the pixel circuit 2.

  During the writing operation, the gate driver 14 uses the gate line in each frame period of the digital image signal DA to write the source signals Sc1, Sc2,..., Scm to each pixel circuit 2 based on the scanning side timing control signal Gtc. GL1, GL2,..., GLn are sequentially selected almost every horizontal period.

  In the self-refresh operation, the gate driver 14 applies the same voltage to all the gate lines GL connected to the target pixel circuit 2 at the same timing under the control of the display control circuit 11 (details are given) Will be described later).

  The counter electrode drive circuit 12 applies a counter voltage Vcom to the counter electrode 80 via the counter electrode wiring CML. In the present embodiment, the counter electrode drive circuit 12 alternately switches and outputs the counter voltage Vcom between a predetermined high level (5 V) and a predetermined low level (0 V) in the normal display mode and the constant display mode. Thus, driving the counter electrode 80 while switching the counter voltage Vcom between the high level and the low level is referred to as “counter AC driving”.

  In the normal display mode, “counter AC drive” switches the counter voltage Vcom between a high level and a low level every horizontal period and every frame period. In other words, in one frame period, the voltage polarity between the counter electrode 80 and the pixel electrode 20 changes in two adjacent horizontal periods. In addition, even in the same one horizontal period, the voltage polarity between the counter electrode 80 and the pixel electrode 20 changes in the two adjacent frame periods.

  On the other hand, in the constant display mode, the same voltage level is maintained during one frame period, but the voltage polarity between the counter electrode 80 and the pixel electrode 20 is changed by two successive writing operations.

  If a voltage having the same polarity is continuously applied between the counter electrode 80 and the pixel electrode 20, the display screen image burn-in (surface image burn-in) occurs. Therefore, a polarity inversion operation is required, but “opposite AC drive” should be adopted. Thus, the voltage amplitude applied to the pixel electrode 20 in the polarity inversion operation can be reduced.

<Pixel circuit>
Next, the configuration of the pixel circuit 2 will be described with reference to FIGS.

  4 to 6 show the basic circuit configuration of the pixel circuit 2 of the present invention. The pixel circuit 2 includes a display element unit 21 including a unit liquid crystal display element Clc, a first switch circuit 22, a second switch circuit 23, a control circuit 24, and an auxiliary capacitance element Cs, which are common to all circuit configurations. It is. The auxiliary capacitive element Cs corresponds to a “second capacitive element”.

  4 corresponds to a basic configuration of each pixel circuit belonging to a group W described later, FIG. 5 corresponds to a basic configuration of each pixel circuit belonging to a group X described later, and FIG. 6 corresponds to a basic configuration of a group Y described later. This corresponds to the basic configuration of the pixel circuit. The unit liquid crystal display element Clc has already been described with reference to FIG. 2 and will not be described.

  The pixel electrode 20 is connected to each end of the first switch circuit 22, the second switch circuit 23, and the control circuit 24 to form an internal node N1. The internal node N1 holds the voltage of pixel data supplied from the source line SL during the write operation.

  The auxiliary capacitance element Cs has one end connected to the internal node N1 and the other end connected to the auxiliary capacitance line CSL. The auxiliary capacitance element Cs is additionally provided so that the internal node N1 can stably hold the voltage of the pixel data.

  In the first switch circuit 22, one end on the side not forming the internal node N1 is connected to the source line SL. The first switch circuit 22 includes a transistor T3 that functions as a switch element. The transistor T3 indicates a transistor whose control terminal is connected to the gate line GL, and corresponds to a “third transistor”. At least when the transistor T3 is off, the first switch circuit 22 is in a non-conductive state, and the conduction between the source line SL and the internal node N1 is cut off.

  The second switch circuit 23 has one end on the side that does not constitute the internal node N1 connected to the voltage supply line VSL. In FIG. 4, the second switch circuit 23 includes a transistor T1. 5 and 6, the second switch circuit 23 is configured by a series circuit of a transistor T1 and a transistor T4.

  The transistor T1 indicates a transistor whose control terminal is connected to the output node N2 of the control circuit 24, and corresponds to a “first transistor element”. The transistor T4 indicates a transistor whose control terminal is connected to the boost line BST or the selection line SEL, and corresponds to a “fourth transistor element”.

  In the configuration of FIG. 4, when the transistor T1 is on, the second switch circuit 23 is in a conductive state, and the voltage supply line VSL and the internal node N1 are in a conductive state. 5 to 6, when both the transistor T1 and the transistor T3 are on, the second switch circuit 23 is in a conductive state, and the voltage supply line VSL and the internal node N1 are in a conductive state.

  The control circuit 24 is configured by a series circuit of a transistor T2 and a boost capacitor element Cbst. A first terminal of the transistor T2 is connected to the internal node N1, and a control terminal is connected to the reference line REF. The second terminal of the transistor T2 is connected to the first terminal of the boost capacitor Cbst and the control terminal of the transistor T1 to form an output node N2. The second terminal of the boost capacitor element Cbst is connected to the boost line BST. The transistor T2 corresponds to a “second transistor element”.

  Incidentally, one end of the auxiliary capacitive element Cs and one end of the liquid crystal capacitive element Clc are connected to the internal node N1. In order to avoid complication of symbols, the capacitance of the auxiliary capacitance element (referred to as “auxiliary capacitance”) is represented as Cs, and the capacitance of the liquid crystal capacitance element (referred to as “liquid crystal capacitance”) is represented as Clc. At this time, the total capacitance parasitic on the internal node N1, that is, the pixel capacitance Cp to which pixel data is to be written and held is substantially represented by the sum of the liquid crystal capacitance Clc and the auxiliary capacitance Cs (Cp≈Clc + Cs).

  At this time, the boost capacitor element Cbst is set so that Cbst << Cp is established if the electrostatic capacity of the element (referred to as “boost capacitor”) is described as Cbst.

  The output node N2 holds a voltage corresponding to the voltage level of the internal node N1 when the transistor T2 is on, and maintains the original holding voltage even when the voltage level of the internal node N1 changes when the transistor T2 is off. The on / off state of the transistor T1 of the second switch circuit 23 is controlled by the holding voltage of the output node N2.

  The four types of transistors T1 to T4 are all thin film transistors such as polysilicon TFTs and amorphous silicon TFTs formed on the active matrix substrate 10. One of the first and second terminals is a drain electrode, and the other is a source. The electrode and the control terminal correspond to the gate electrode. Furthermore, each of the transistors T1 to T4 may be composed of a single transistor element. However, when there is a high demand for suppressing a leakage current when the transistor is off, a plurality of transistors are connected in series and a control terminal is shared. May be configured. In the following description of the operation of the pixel circuit 2, it is assumed that the transistors T1 to T4 are all N-channel polysilicon TFTs and have a threshold voltage of about 2V.

  The pixel circuit 2 can have various circuit configurations as will be described later, and these can be patterned as follows.

  1) First, as described above, with regard to the configuration of the second switch circuit 23, there are two possible cases: the case where the second switch circuit 23 is constituted by only the transistor T1, and the case where the second switch circuit 23 is constituted by a series circuit of the transistors T1 and T4. The former corresponds to group W (FIG. 4), and the latter corresponds to group X (FIG. 5) and group Y (FIG. 6). Of the latter, the configuration in which the control terminal of the transistor T4 is connected to the boost line BST is group Y, and a selection line SEL is provided separately from the boost line BST, and the control terminal of the transistor T4 is provided on the selection line SEL. The connected configuration is group X.

  2) As for the first switch circuit 22, in the case where it is constituted by only the transistor T3, in the case where it is constituted by a series circuit of another transistor element whose conduction is controlled by a signal line other than the gate line GL, Two ways are possible. In the latter case, as another transistor element constituting the series circuit, the transistor T4 in the second switch circuit 23 can be used, or the transistor T4 in the second switch circuit 23 and the control terminal are connected to each other. Another transistor element may be used.

  3) With respect to the voltage supply line VSL, there are three possible ways: an independent signal line, a common line shared with the source line SL, or a common line shared with the auxiliary capacitance line CSL. . Details will be described later.

  In the following, the pixel circuits 2 are organized by type based on the above 1) to 3). As described above, the basic type structure is divided into three groups (W, X, Y), and the combination of the configuration of the voltage supply line VSL and the configuration of the first switch circuit 22 is described for each group.

<1. Group W>
A group W in which the second switch circuit 23 includes only the transistor T1 will be described.

  First, for the group W, when the voltage supply line VSL is also used as the source line SL, the auxiliary capacitance line CSL, or the gate line GL, a pixel circuit cannot be configured. This is because such a pixel circuit cannot perform a writing operation correctly.

  For example, the case where the voltage supply line VSL is also used as the source line SL will be described as an example. As will be described later, high and low binary voltages (5 V, 0 V) are written in the constant display mode in the present invention. As described in the third embodiment, during the write operation, a high voltage is applied to the reference line REF and the transistor T2 is turned on. For this reason, the potential VN2 of the node N2 is also 5V. It is assumed that 0 V is written to another pixel circuit that shares the pixel circuit and the source line SL. At this time, 0 V is applied to the source line SL. At this time, the transistor T1 becomes conductive in the direction from the node N1 toward the source line SL, and the potential of the node N1 decreases. In other words, the written potential is not correctly held, which means that the writing operation cannot be performed correctly.

  The same can be said for the case where the voltage supply line VSL is also used as the auxiliary capacitance line CSL and the gate line GL. This is because it is assumed that 0 V is applied to these lines.

  On the other hand, when the voltage supply line VSL is an independent signal line, by applying a high voltage to the voltage supply line VSL, it is possible to prevent the potential of the node N1 to which high level writing has been performed from being lowered. be able to. That is, as described later in the third embodiment, it is necessary to apply a high level voltage to the voltage supply line VSL during the write operation.

  Also, the pixel circuit cannot be configured when the voltage supply line VSL is also used as the reference line REF or the boost line BST. Each pixel circuit included in the display device of the present invention is characterized in that a self-refresh operation described later in the second embodiment can be performed, but is also used as the voltage supply line VSL reference line REF or the boost line BST. This is because this self-refresh operation cannot be executed. The same applies to the groups X and Y.

  In the pixel circuit 2A shown in FIG. 7, the voltage supply line VSL is configured by an independent signal line. For example, the reference line REF and the voltage supply line VSL extend in the horizontal direction (row direction) in parallel with the gate line GL, but may extend in the vertical direction (column direction) in parallel with the source line SL.

<2. Group X>
A group X in which the second switch circuit 23 is configured by a series circuit of transistors T1 and T4 and the control terminal of the transistor T4 is connected to the selection line SEL will be described. That is, the selection line SEL is added as compared with the configuration of the group W.

  In the case of the group X, unlike the group W, the second switch circuit 23 includes the transistor T4 in addition to the transistor T1, and the second switch circuit 23 is turned off by turning off the transistor T4 of the pixel circuit that is not a write target. Circuit 23 can be turned off. Therefore, unlike the group W, the write operation can be performed correctly even if the voltage supply line VSL is shared with the source line SL and the auxiliary capacitance line CSL. On the other hand, the voltage supply line cannot be used as the gate line GL, the reference line REF, and the boost line BST for the same reason as the group W.

  Hereinafter, the case where the first switch circuit 22 is configured by the transistor T3 alone will be described as first to third types. Among these, the case where the voltage supply line VSL is an independent signal line is the first type, the case where the voltage supply line VSL is also used as the source line SL, the second type, and the voltage supply line VSL is also used as the auxiliary capacitance line CSL. The case is the third type.

  The case where the first switch circuit 22 is constituted by a series circuit of a transistor T3 and another transistor element whose conduction is controlled by a signal line other than the gate line GL will be described as fourth to fifth types. Among these, a case where the voltage supply line VSL is an independent signal line is a fourth type, and a case where the voltage supply line VSL is also used as the source line SL is a fifth type. It should be noted that the case where the transistor T3 is configured by a series circuit of another transistor element whose conduction is controlled by a signal line other than the gate line GL, and the voltage supply line VSL is also used as the auxiliary capacitance line CSL is separately implemented. This will be described as an example.

(First to third types)
First, the first to third types in which the first switch circuit 22 is constituted by the transistor T3 alone will be described.

  In the first type pixel circuit 2B shown in FIG. 8, the first switch circuit 22 is constituted only by the transistor T3, and the voltage supply line VSL is constituted by an independent signal line. For example, the reference line REF and the voltage supply line VSL extend in the horizontal direction (row direction) in parallel with the gate line GL, but may extend in the vertical direction (column direction) in parallel with the source line SL.

  Here, in FIG. 8, the second switch circuit 23 is configured by a series circuit of a transistor T1 and a transistor T4. As an example, the first terminal of the transistor T1 is connected to the internal node N1, and the second terminal of the transistor T1 is A configuration example is shown in which the first terminal of the transistor T4 is connected and the second terminal of the transistor T4 is connected to the voltage supply line VSL. However, the arrangement of the transistors T1 and T4 in the series circuit may be switched, and a circuit configuration in which the transistor T1 is sandwiched between the two transistors T4 may be employed. The two modified circuit configuration examples are shown in FIGS.

  In the second type pixel circuit 2C shown in FIG. 11, the first switch circuit 22 is configured only by the transistor T3, and the voltage supply line VSL is shared with the source line SL.

  In the third type pixel circuit 2D shown in FIG. 12, the first switch circuit 22 is configured only by the transistor T3, and the voltage supply line VSL is shared with the auxiliary capacitance line CSL. For example, the storage capacitor line CSL extends in the horizontal direction (row direction) in parallel with the gate line GL, but may extend in the vertical direction (column direction) in parallel with the source line SL.

  In these second to third types, as in the case of the first type, it is possible to realize a modified circuit corresponding to the configuration of the second switch circuit 23 as shown in FIGS.

(4th to 5th type)
Next, each type of pixel circuit in which the first switch circuit 22 is configured by a series circuit of the transistor T3 and other transistor elements will be described.

  A pixel circuit 2E of the fourth type shown in FIG. 13 is similar to the pixel circuit 2B of the first type shown in FIG. 8 except that the first switch circuit 22 is composed of a series circuit of a transistor T3 and another transistor element. It is common.

  Here, FIG. 13 shows a configuration in which a transistor in the second switch circuit 23 is also used as a transistor element other than the transistor T3 constituting the first switch circuit 22. That is, the first switch circuit 22 is configured by a series circuit of a transistor T3 and a transistor T4, and the second switch circuit 23 is configured by a series circuit of a transistor T1 and a transistor T4. The first terminal of the transistor T4 is connected to the internal node N1, the second terminal of the transistor T4 is connected to the first terminal of the transistor T1 and the first terminal of the transistor T3, and the second terminal of the transistor T3 is the source line SL. The second terminal of the transistor T1 is connected to the voltage supply line VSL.

  That is, in the fourth type pixel circuit 2E, the first switch circuit 22 is configured to be conductively controlled by the selection line SEL in addition to the gate line GL.

  As a variation of the fourth type, as shown in FIG. 14, as a transistor element other than the transistor T3 constituting the first switch circuit 22, a transistor T5 in the second switch circuit 23 and a transistor T5 connected between control terminals are connected. It is also possible to realize a configuration using. The transistor T5 corresponds to a “fifth transistor element”.

  In the pixel circuit 2E shown in FIG. 14, since the control terminals of the transistor T5 and the transistor T4 are connected to each other, the transistor T5 is ON / OFF controlled by the selection line SEL similarly to the transistor T4. The transistor elements other than the transistor T3 configuring the first switch circuit 22 are common to the configuration of FIG. 13 in that on / off control is performed by the selection line SEL.

  In the pixel circuit 2E shown in FIG. 13, the transistor T4 is shared by the first switch circuit 22 and the second switch circuit 23. In such a circuit configuration, the transistor T4 in the second switch circuit 23 needs to be positioned on the internal node N1 side, and the transistor T1 must be positioned on the voltage supply line VSL side, and the positional relationship between the transistors T1 and T4 is illustrated. It cannot be reversed as in 8. On the other hand, as shown in FIG. 10, the transistor T1 can be sandwiched between the transistors T4. A modification in this case is shown in FIG.

  On the other hand, in the case of the configuration shown in FIG. 14, the arrangement of the transistors T3 and T5 in the first switch circuit 22 is changed, and the arrangement of the transistors T1 and T4 in the second switch circuit 23 is changed. Such a modification is possible.

  A fifth type pixel circuit 2F shown in FIG. 17 is obtained by configuring the first switch circuit 22 as a series circuit of a transistor T4 and a transistor T3 in the second type pixel circuit 2C shown in FIG. In the case of the fifth type, both the first switch circuit 22 and the second switch circuit 23 are configured to connect one to the internal node N1 and the other to the source line SL. Therefore, as shown in FIG. The arrangement of the transistor elements T1 and T4 in the circuit 23 can be switched. Furthermore, a modified circuit as shown in FIG. 19 is also possible. Naturally, it is possible to realize a modified circuit as shown in FIGS. 14 to 16 of the fourth type. In the fifth type pixel circuit, the selection line SEL is configured in parallel with the gate line GL.

<3. Group Y>
A group Y in which the second switch circuit 23 is configured by a series circuit of transistors T1 and T4 and the control terminal of the transistor T4 is connected to the boost line BST will be described. In other words, this group Y has a configuration in which the selection line SEL is eliminated from the configuration of the group X, and the boost line BST also serves as the selection line SEL.

  Similarly to the group X, the group Y includes the transistor T4. Therefore, even if the voltage supply line VSL is also used as the source line SL or the auxiliary capacitance line CSL, the writing operation is not hindered. On the other hand, the reason why the voltage supply line cannot be shared with the gate line GL, the reference line REF, and the boost line BST is the same as the groups W and X.

  In the group Y, the configuration in which the voltage supply line VSL is an independent signal line when the first switch circuit 22 is configured by the transistor T3 alone is the first type, and the voltage supply line VSL is the source line. The case where SL is also used is the second type. In the case where the first switch circuit 22 is configured by a series circuit of another transistor element whose conduction is controlled by a signal line other than the transistor T3 and the gate line GL, the voltage supply line VSL is an independent signal following the group X. A configuration that is a line is a fourth type, and a case that is also used as a source line SL is a fifth type. A configuration in the case where the voltage supply line VSL is also used as the auxiliary capacitance line CSL will be described in another embodiment.

  That is, the group Y first-type pixel circuit connects the control terminal of the transistor T4 to the boost line BST and connects the selection line SEL to the group X first-type pixel circuit (FIGS. 8 to 10). Corresponds to the lost configuration. A configuration corresponding to FIG. 8 is shown in FIG. In each drawing of the pixel circuits of group Y, the corresponding relationship is clarified by using the corresponding alphabet in the code of group X replaced with lower case letters. In FIG. 20, the pixel circuit 2b is indicated.

  The second type pixel circuit 2c can be configured to correspond to the second type pixel circuit 2C of group X, and an example thereof is shown in FIG. The fourth type pixel circuit 2e can be configured to correspond to the fourth type pixel circuit 2E of group X, and an example thereof is shown in FIG. The fifth type pixel circuit 2f can be configured to correspond to the fifth type pixel circuit 2F of group X, an example of which is shown in FIG.

  In each pixel circuit belonging to the group Y, a modified circuit similar to the pixel circuit of the same type described above in the group X can be realized.

[Second Embodiment]
In the second embodiment, the self-refresh operation by the pixel circuits of the groups W, X, and Y described above will be described with reference to the drawings.

  The self-refresh operation is an operation in the constant display mode, and the first switch circuit 22, the second switch circuit 23, and the control circuit 24 are operated in a predetermined sequence for the plurality of pixel circuits 2, and the potential of the pixel electrode 20 is determined. (This is also the potential of the internal node N1) is an operation for simultaneously restoring the potential written in the previous write operation in a lump. The self-refresh operation is an operation peculiar to the present invention by each of the pixel circuits described above, and consumes significantly less energy than the “external refresh operation” in which the normal write operation is performed to restore the potential of the pixel electrode 20 as in the past. Electricity is possible. Note that “simultaneously” in the above “collectively” means “simultaneously” having a time width of a series of self-refresh operations.

  By the way, conventionally, a write operation is performed, and an operation of inverting only the polarity (external polarity inversion operation) while maintaining the absolute value of the liquid crystal voltage Vcl applied between the pixel electrode 20 and the counter electrode 80 is performed. It was. When this external polarity inversion operation is performed, the polarity is inverted and the absolute value of the liquid crystal voltage Vcl is also updated to the state at the time of the previous writing. That is, polarity inversion and refresh are performed simultaneously. For this reason, the refresh operation is not usually performed for the purpose of updating only the absolute value of the liquid crystal voltage Vcl without inverting the polarity by the write operation. From the viewpoint of comparison with the refresh operation, such a refresh operation is referred to as an “external refresh operation”.

  Even when the refresh operation is executed by the external polarity inversion operation, the write operation is not changed. That is, even when compared with this conventional method, the power consumption can be greatly reduced by the self-refresh operation of this embodiment.

  All gate lines GL, source lines SL, reference lines REF, auxiliary capacitance lines CSL, boost lines BST, and counter electrodes 80 connected to the pixel circuit 2 to be subjected to the self-refresh operation are all applied with voltage at the same timing. Done. In the case where the selection line SEL is provided, when the voltage supply line VSL is provided as an independent signal line, the voltage is applied to these signal lines at the same timing. Under the same timing, the same voltage is applied to all the gate lines GL, the same voltage is applied to all the reference lines REF, and the same voltage is applied to all the auxiliary capacitance lines CSL. The same voltage is applied to all boost lines BST. When the selection line SEL and the voltage supply line VSL are provided as independent signal lines, the same voltage is applied to all the selection lines SEL, and the same voltage is applied to all the voltage supply lines VSL. . The timing control of the voltage application is performed by the display control circuit 11, and each voltage application is performed by the display control circuit 11, the counter electrode drive circuit 12, the source driver 13, and the gate driver 14.

  In the constant display mode of the present embodiment, pixel data of two gradations (binary) is held in pixel circuit units, so that the potential VN1 (voltage VN1) held in the pixel electrode 20 (internal node N1) is Two voltage states are shown, one voltage state and the second voltage state. In the present embodiment, similarly to the above-described counter voltage Vcom, the first voltage state is described as a high level (5V) and the second voltage state is described as a low level (0V).

  In the state immediately before the execution of the self-refresh operation, it is assumed that both the pixel in which the pixel electrode 20 is written at the high level voltage and the pixel in which the pixel electrode 20 is written at the low level voltage are mixed. However, according to the self-refresh operation of the present embodiment, the refresh operation for all the pixel circuits is executed by performing the voltage application process based on the same sequence regardless of whether the pixel electrode 20 is written to a high or low voltage. can do. This will be described with reference to timing diagrams and circuit diagrams.

  In the following description, the voltage (high level voltage) in the first voltage state is written in the immediately preceding write operation, and the case where the high level voltage is restored is referred to as “case H”. A case where the voltage state (low level voltage) is written and the low level voltage is restored is referred to as “case L”.

<1. Group W>
First, the self-refresh operation of the pixel circuits belonging to the group W will be described for each type.

  An example of a timing diagram of the self-refresh operation by the pixel circuit 2A (FIG. 7) is shown in FIG. In FIG. 24, the voltage waveforms of all the gate lines GL, source lines SL, reference lines REF, auxiliary capacitance lines CSL, voltage supply lines VSL, and boost lines BST connected to the pixel circuit 2A to be subjected to the self-refresh operation, The voltage waveform of the counter voltage Vcom is illustrated. In the present embodiment, all the pixel circuits in the pixel circuit array are subjected to the self-refresh operation.

  Further, FIG. 24 shows waveforms indicating changes in the potential (pixel voltage) VN1 of the internal node N1 and the potential VN2 of the output node N2 in cases H and L, and the on / off states of the transistors T1 to T3. In FIG. 24, which case corresponds to the case with parentheses, for example, VN1 (H) is a waveform indicating a change in potential VN1 in case H.

  It is assumed that high-level writing is performed in case H and low-level writing is performed in case L at a time before the time (t0) when the self-refresh operation is started.

  In the following timing diagrams, the times t0 to t9 are shown as being equally spaced for convenience, but these time intervals need not be equally spaced.

  When a time elapses after the write operation is performed without performing the self-refresh operation, the potential VN1 of the internal node N1 varies with the occurrence of a leakage current of each transistor in the pixel circuit. In case H, VN1 was 5 V immediately after the write operation, but this value is lower than the initial value as time elapses. This is mainly due to leakage current flowing toward a low potential (for example, a ground line) through an off-state transistor.

  In case L, the potential VN1 was 0 V immediately after the write operation, but it may rise slightly over time. This is because, for example, a write voltage is applied to the source line SL during a write operation to another pixel circuit, so that even a non-selected pixel circuit is internally connected from the source line SL via a non-conductive transistor. This is because a leak current flows toward the node N1.

  In FIG. 24, at time t0, VN1 (H) is displayed slightly lower than 5V and VN1 (L) is displayed slightly higher than 0V. These take the above potential fluctuations into consideration.

  At time t0, 5V is applied to the reference line REF. This voltage is such that when the voltage state (potential state) of the internal node N1 is high (case H), the transistor T2 is non-conductive, and when it is low (case L), the transistor T2 is conductive. Such a voltage value. This applied voltage corresponds to the “first control voltage”.

  A voltage is applied to the gate line GL so that the transistor T3 is completely turned off. Here, it is set to -5V. This applied voltage corresponds to the “first scanning voltage”.

  A voltage (0 V) corresponding to the second voltage state is applied to the source line SL. In the pixel circuit 2A, the voltage applied to the source line SL can be constantly set to 0 V during the self-refresh operation.

  The counter voltage Vcom applied to the counter electrode 80 and the voltage applied to the storage capacitor line CSL are set to 0V. This is not limited to 0V, and the voltage value at the time prior to time t0 may be maintained as it is.

  The boost line BST is applied with 0V as an initial voltage at time t0. A voltage (5 V) in the first voltage state is applied to the voltage supply line VSL. Although described as another embodiment, the voltage applied to the voltage supply line VSL from time t0 to t3 is not necessarily limited to 5V.

  At time t1, the voltage applied to boost line BST is increased. In this embodiment, the voltage is 10V. This value is such that the transistor T1 is turned on when the voltage state of the node N1 is at a high level (case H), and the transistor T1 is turned off when it is at a low level (case L). This corresponds to the “first boost voltage”.

  The boost line BST is connected to one end of the boost capacitor element Cbst. Therefore, when a high level voltage is applied to the boost line BST, the potential at the other end of the boost capacitor element Cbst, that is, the potential at the output node N2 is pushed up. In this way, raising the potential of the output node N2 by increasing the voltage applied to the boost line BST is hereinafter referred to as “boost pushing up”.

  As described above, in case H, the transistor T2 is non-conductive at time t1. For this reason, the potential fluctuation amount of the node N2 due to boost boosting is determined by the ratio of the boost capacitance Cbst to the total capacitance parasitic on the node N2. As an example, if this ratio is 0.7, if one electrode of the boost capacitor increases by ΔVbst, the other electrode, that is, the node N2, increases by approximately 0.7ΔVbst.

  At time t1, 5 V is applied to the reference line REF. Therefore, as in the case of time t0, in the case H, the transistor T2 is non-conductive. For this reason, the potential fluctuation amount of the node N2 due to boost boosting is determined by the ratio of the boost capacitance Cbst and the total capacitance parasitic on the node N2. As an example, if this ratio is 0.7, if one electrode of the boost capacitor increases by ΔVbst, the other electrode, that is, the node N2, increases by approximately 0.7ΔVbst.

  Since internal node potential VN1 (H) at time t1 is approximately 5 V, transistor T1 becomes conductive when a potential higher than threshold voltage 2V higher than VN1 is applied to the gate of transistor T1, that is, output node N2. In this embodiment, the voltage applied to the boost line BST at time t1 is 10V. In this case, the output node N2 rises by 7V. Since the potential VN2 (H) of the output node N2 is substantially the same potential (5V) as VN1 (H) at the time immediately before time t1, the node N2 shows about 12V by boosting. Therefore, since a potential difference equal to or higher than the threshold voltage is generated between the gate and the node N1 in the transistor T1, the transistor T1 is turned on. To represent this, in FIG. 24, T1 (H) at times t1 to t2 is described as “ON”.

  On the other hand, in case L, the transistor T2 is conductive at time t1. That is, unlike the case H, the output node N2 and the internal node N1 are electrically connected. In this case, the fluctuation amount of the potential VN2 (L) of the output node N2 due to boost boosting is affected by the total parasitic capacitance of the internal node N1 in addition to the boost capacitance Cbst and the total parasitic capacitance of the node N2.

  One end of the auxiliary capacitive element Cs and one end of the liquid crystal capacitive element Clc are connected to the internal node N1, and the total capacitance Cp parasitic on the internal node N1 is substantially represented by the sum of the liquid crystal capacitance Clc and the auxiliary capacitance Cs. As described above. The boost capacitance Cbst is much smaller than the liquid crystal capacitance Cp. Therefore, the ratio of the boost capacity to the total capacity is extremely small, for example, a value of about 0.01 or less. In this case, if one electrode of the boost capacitor element rises by ΔVbst, the other electrode, that is, the output node N2 rises by about 0.01ΔVbst at most. That is, even when ΔVbst = 10V, the potential VN2 (L) of the output node N2 hardly rises. Therefore, the transistor T1 is still non-conductive from time t1 to t2. To represent this, in FIG. 24, T1 (L) at times t1 to t2 is described as “OFF”.

  As described above, by boost boosting at time t1, the transistor T1 of the case H is turned on. In this embodiment, since 5 V is applied to the voltage supply line VSL at time t1, in case H, this 5 V is supplied to the node N1 via the transistor T1. That is, the node N1 (H) is refreshed to 5V (see the waveform of VN1 (H) at times t1 to t2). However, as will be described later, since the potential VN1 of the node N1 is forcibly refreshed to 0 V after that, the refresh operation in this time period is not so meaningful, and as the progress of the entire refresh operation, it is temporarily Only refreshed to 5V. Note that during this period, the transistor T2 (H) is non-conductive, so that the potential VN2 (H) of the node N2 maintains the previous potential.

  At time t2, the voltage applied to the reference line REF is reduced to 0V. This value may be a voltage that makes the transistor T2 non-conductive in both cases H and L, and corresponds to the “second control voltage”. The voltage of the reference line REF is maintained thereafter until time t7, and the transistor T2 is in a non-conductive state until the same time in both cases H and L. Since transistor T2 is rendered non-conductive, potential VN2 of output node N2 is maintained without being affected by fluctuations in potential VN1 of internal node N1.

  At time t3, the voltage supply line VSL is lowered to the second voltage state (0 V). Even at this time, since the transistor T1 in the case H is still conductive, a current path from the internal node N1 to the voltage supply line VSL through the transistor T1 is formed, and VN1 (H) is in the second voltage state. It drops to (0V). Note that since the transistor T2 (H) is non-conductive, the potential VN2 (H) of the output node N2 still maintains the immediately preceding potential.

  At time t4, the voltage applied to the gate line GL is increased, and the transistor T3 is turned on in both case H and case L. Here, 5 V was applied. This applied voltage corresponds to the “second scanning voltage”. As a result, the source line SL to which the voltage (0V) in the second voltage state is applied and the internal node N1 become conductive, so that the potential VN1 of the internal node N1 is set to the second voltage state (0V) in both cases H and L. Refreshed. At this time, since the transistor T2 is non-conductive in both cases, the potential VN2 of the output node N2 is not refreshed and still maintains the previous potential.

  At time t5, the voltage applied to the gate line GL is decreased again (−5V), and the transistor T3 is turned off. In both cases H and L, the potential VN1 of the internal node N1 is maintained as it was just refreshed (0 V).

  At time t6, the voltage of the first voltage state (5 V) is applied to the voltage supply line VSL. In case H, since the potential of the output node N2 is still maintained at a high level even at this time, the transistor T1 is still conducting. Therefore, in case H, a current path from the voltage supply line VSL to the internal node N1 through the transistor T1 is formed, and the internal node N1 (H) is refreshed to the first voltage state (5V). On the other hand, in the case L, since the output node VN2 is in the low level state and the transistor T1 is non-conductive, 5V applied to the voltage supply line VSL is not applied to the internal node N1.

  That is, between times t4 and t5, both cases are refreshed to the second voltage state with respect to internal node N1, and thereafter between times t6 and t7, only the case H is refreshed to the first voltage state. . As a result, the refresh operation is performed in both cases.

  After time t7, so-called post-processing after the refresh operation is performed. At time t7, 8V is applied to the reference line REF. This is for the purpose of turning on the transistor T2 in both cases H and L, and for the purpose of copying the refreshed potential of the internal node N1 to the output node N2. As described above, since the parasitic capacitance of the internal node N1 is much larger than the parasitic capacitance of the output node N2, even if the internal node N1 and the output node N2 are connected, the potential VN1 of the internal node N1 is equal to the potential of the output node N2. On the contrary, VN2 is transferred to VN1 without being affected by VN2. As a result, the refreshed potential is held at the output node N2 in both cases. That is, VN2 (H) is 5V and VN2 (L) is 0V.

  At time t8, the voltage applied to the boost line BST is reduced to 0V. At this point, the transistor T2 is conductive in both cases, and the output node N2 and the internal node N1 are connected. As described above, since the parasitic capacitance of the internal node N1 is much larger than the capacitance of the boost capacitor element, VN1 and VN2 are hardly affected by the fluctuation of the voltage applied to the boost line BST, and the potential just before Is kept as it is.

  Thereafter, at time t9, the voltage applied to the reference line REF is returned to 5V. As a result, the voltage applied to each line becomes the same as that at time t0. After waiting for a while in this state, the self-refresh operation is repeatedly executed by repeating the operation from time t1 to t9 again.

  When the refresh operation is performed by writing by applying a voltage via the source line SL as in the prior art, it is necessary to scan the gate lines GL one by one in the vertical direction. For this reason, it is necessary to apply a high level voltage to the gate line GL by the number (n) of the gate lines. In addition, since it is necessary to apply the same potential level as the potential level written in the immediately preceding write operation to each source line SL, each source line SL needs to be charged and discharged a maximum of n times. To do.

  On the other hand, according to the present embodiment, the voltage application control as shown in FIG. 24 is executed for each of the gate line GL, the boost line BST, the reference line REF, and the voltage supply line VSL at times t1 to t9. In addition, thereafter, by keeping the potential of each line constant, the internal node potential VN1 (the potential of the pixel electrode 20) can be returned to the potential state at the time of the writing operation for all the pixels. . In particular, according to the method of the present invention, the self-refresh operation can be directly executed for both the first voltage state and the second voltage state.

  Therefore, according to the self-refresh operation of the present embodiment, the number of times of voltage application to the gate line GL and voltage application to the source line SL can be greatly reduced as compared with the normal external refresh operation, and the control content is also improved. It can be simplified. For this reason, the power consumption of the gate driver 14 and the source driver 13 can be greatly reduced.

The self-refresh operation of this embodiment is summarized as follows. Note that # 1 to # 6 indicate step numbers.
(# 1) The applied voltage to the reference line REF is changed to turn off the case T transistor T2 and turn on the case L transistor T2. The transistor T3 is kept off.
(# 2) The boost voltage is changed by changing the voltage applied to the boost line BST, and the transistor T1 of the case H is turned on. In case L, since the transistor T2 is conductive, the potential of the output node N2 hardly changes, and the transistor T1 still maintains the off state.
(# 3) The voltage applied to the reference line REF is changed to turn off the transistor T2 in both cases H and L.
(# 4) The voltage (0V) in the second voltage state is applied to the source line SL, the applied voltage to the gate line GL is changed to turn on the transistor T3, and the internal node N1 is set to the second voltage state in both cases. Refresh.
(# 5) After changing the voltage applied to the gate line GL to turn off the transistor T3, 5V is applied to the voltage supply line VSL, and the internal node N1 is connected only to the case H in which the transistor T1 is conducting. Refresh to the first voltage state. In case L, the transistor T1 is non-conductive, so that the applied voltage (5 V) to the voltage supply line VSL is not supplied to the internal node N1.
(# 6) The voltage applied to the boost line BST is restored. Further, the voltage applied to the reference line REF is changed to make the transistor T2 conductive in both cases H and L, and the potential of the internal node N1 is copied to the output node N2.

  In addition, another embodiment (modified example) as described below is also possible.

  1) In the above embodiment, the voltage (0 V) corresponding to the second voltage state is always applied to the source line SL, but the second voltage is at least when the transistor T3 is conductive (time t4 to t5: step # 4). It suffices if the voltage of the state is applied. However, in the sense that unnecessary voltage fluctuations can be avoided, it is preferable to hold 0 V over the period of the self-refresh operation as in the above embodiment.

  2) In the above embodiment, after the refresh operation for the case H is completed, the transistors T2 in both cases (H, L) are turned on at time t7, and then the voltage applied to the boost line BST is lowered at time t8. . However, after the voltage applied to the boost line BST is reduced at time t7, the transistors T2 in both cases (H, L) may be turned on at time t8 (see FIG. 25).

  In this case, since the transistor T2 is non-conductive in both cases when the applied voltage of the boost line BST is lowered, the potential of the node N2 at time t7 to t8 as the applied voltage of the boost line BST is lowered. After that, the transistor T2 becomes conductive at time t8, so that the potential VN1 of the internal node N1 after refresh is supplied to the output node N2, and VN2 is the same as VN1. Value. Since the parasitic capacitance of the internal node N1 is much larger than the parasitic capacitance of the output node N2, the potential VN1 of the internal node N1 is hardly affected even if the potential of the output node N2 is lowered. As described above.

  In case H, the potential VN2 of the output node N2 drops to the potential before the execution of the self-refresh operation (time t0) at the time t7. In this respect, the mode is different from that in FIG. At time t8, 8V is applied to the reference line REF to turn on the transistor T2, so that the potential VN1 (H) of the internal node N1 refreshed to the first voltage state is applied. As a result, VN2 (H) is also refreshed. A later first voltage state (5 V) is obtained.

  In the case L, at time t7, the potential VN2 of the output node N2 is significantly lower than the potential before execution of the self-refresh operation (at time t0). Although different, as in the case H, when the transistor T2 becomes conductive at time t8, the potential VN1 (L) of the internal node N1 refreshed to the second voltage state is given, and as a result, VN2 (L) is also refreshed In the second voltage state (0V).

  3) After time t8, after the refresh operation is completed, it becomes a waiting period until the refresh operation is executed again. In the above embodiment, the applied voltage of the reference line REF is set to 5 V at time t9. This means that the standby is performed with 5 V applied to the reference line REF. However, it is not always necessary to wait in a state where 5 V is applied to the reference line REF. For example, after the voltage applied to the reference line REF is reduced to 0 V at time t9, it is possible to wait until the next self-refresh operation is performed in this state. At this time, when the next self-refresh operation is performed, the voltage applied to the reference line REF is set to 5 V at time t0.

  4) In FIG. 24, 0 V is applied to the voltage supply line VSL from time t4 to t5. Instead of this, it is theoretically possible to apply 5 V to the voltage supply line VSL during the same period. This method will be described later in another embodiment.

<2. Group X>
Next, the self-refresh operation of the pixel circuits belonging to the group X will be described for each type.

(First type)
The first type pixel circuit 2B (FIGS. 8 to 10) differs from the group W pixel circuit 2A only in that it includes a transistor T4. If so, the voltage state can be made exactly the same as that of the first-type pixel circuit 2A of the group W described above, as long as the transistor T4 is kept conductive at least during the self-refresh operation period. In this case, the timing diagram is as shown in FIG. FIG. 26 also shows the conduction state of the transistor T4. Note that 10 V was applied to the selection line SEL in order to make the transistor T4 conductive. A description of the operation is omitted. 26 shows the case where the voltage state is exactly the same as that in the timing diagram of FIG. 24, it is naturally possible to have the same voltage state as in FIG.

  Other voltage application methods are possible. As described in the group W, the voltage of the first voltage state (5V) is supplied from the voltage supply line VSL in a state where the first switch circuit 22 is turned off in step # 5 and the second switch circuit 23 is turned on only in the case H. ) To the internal node N1, only the case H is refreshed to the first voltage state. Therefore, the transistor T4 only needs to be conducted at least during step # 5, and it is not always necessary to turn it on. FIG. 27 shows a timing chart when the transistor T4 is turned on only during step # 5 (time t6 to t7) with respect to the timing chart of FIG.

  Thus, in this group X, the on / off control of the second switch circuit 23 can also be realized by the transistor T4. Accordingly, in step # 4 (time t4 to t5), when the 0V refresh is performed from the source line SL to the internal node N1, the transistor T4 is turned off even if 5V is applied to the voltage supply line VSL. By doing so, the internal node N1 and the voltage supply line VSL can be electrically disconnected. Therefore, in the first type pixel circuit 2B of group X, the applied voltage to the voltage supply line VSL can be fixed to 5 V over the self-refresh operation period. FIG. 28 shows a timing chart in this case.

(Type 2)
The second type pixel circuit 2C (FIG. 11) is different from the pixel circuit 2B in that the voltage supply line VSL is also used as the source line SL. Therefore, only during at least step # 5 (time t6 to t7), a high level voltage is applied to the selection line SEL to turn on the transistor T4, and the applied voltage to the source line SL is a timing chart in the first type pixel circuit 2B ( What is necessary is just to make it the same as the applied voltage of the voltage supply line VSL shown in FIG. An example is shown in FIG.

  Further, the voltage applied to the source line SL may be 5 V only during step # 5 (time t6 to t7) for refreshing to the first voltage state, and may be 0 V in other time zones. A timing chart in this case is shown in FIG.

(3rd type)
In the third type pixel circuit 2D (FIG. 12), the auxiliary capacitance line CSL is also used as the voltage supply line VSL. The auxiliary capacitance line CSL is connected to one end of the auxiliary capacitance element CS, and this capacitance occupies a large proportion with respect to the parasitic capacitance of the internal node N1. For this reason, if the voltage applied to the auxiliary capacitance line CSL fluctuates during the self-refresh operation period, the potential VN1 of the internal node N1 also fluctuates, which is not preferable. Therefore, a constant voltage is applied to the auxiliary capacitance line CSL during the self-refresh operation period. In this type, since the auxiliary capacitance line CSL is also used as the voltage supply line VSL, it is fixed to the first voltage state (5 V) during the self-refresh period.

  In the case of the circuit configuration of this group X, the point that the refresh operation can be correctly realized even when the voltage applied to the voltage supply line VSL is fixed to 5 V is as described with reference to FIG. For the same reason, in the third type pixel circuit 2D, the self-refresh operation can be executed by fixing the voltage applied to the auxiliary capacitance line CSL to 5V. A timing chart in this case is shown in FIG. In FIG. 31, “5 V (limited)” is written in the column of the voltage applied to the auxiliary capacitance line CSL to clearly indicate that 0 V cannot be adopted as the voltage applied to the auxiliary capacitance line CSL.

(4th type)
The fourth type pixel circuit 2E (FIGS. 13 to 16) is common to the first type pixel circuit 2B in that the voltage supply line VSL is formed of an independent signal line. On the other hand, the transistor T4 is different in that the first switch circuit 22 and the second switch circuit 23 are shared.

  Referring to the timing chart of the first type shown in FIG. 27, it can be seen that the first switch circuit 22 is turned on at times t4 to t5 and the second switch circuit 23 is turned on at times t6 to t7. That is, in order to apply the voltage (0 V) of the second voltage state from the source line SL to the internal node N1 in step # 4 and refresh to the second voltage state, the first switch circuit 22 needs to be turned on. In order to refresh the first voltage state by applying the voltage (5V) in the first voltage state from the voltage supply line VSL to the internal node N1 of the case H at 5 in FIG. Therefore, in the case of the fourth type pixel circuit 2E, it is understood that the transistor T4 should be turned on at least between the times t4 to t5 and the times t6 to t7 with respect to the timing chart of FIG.

  Based on this, a timing chart of the fourth type pixel circuit 2E is shown in FIG. In FIG. 32, by applying a high level voltage to the selection line SEL from time t4 to t7, the transistor T4 is made conductive during the synchronization.

  In the case where the voltage application to the voltage supply line VSL is made the same as in FIG. 32, a high level voltage may be applied to the selection line SEL during the self-refresh operation period as shown in FIG.

(5th type)
The fifth type pixel circuit 2F (FIGS. 17 to 19) is common to the second type pixel circuit 2C in that the voltage supply line VSL is also used as the source line SL. On the other hand, the transistor T4 is different in that the first switch circuit 22 and the second switch circuit 23 are shared.

  Referring to the timing chart of the second type shown in FIG. 29, as in the first type, the first switch circuit 22 is turned on from time t4 to t5, and the second switch circuit 23 is turned on from time t6 to t7. I understand that. Therefore, for the same reason as the fourth type, it is understood that the transistor T4 should be made conductive at least from time t4 to t5 and from time t6 to t7. FIG. 33 shows an example of a timing chart of the fifth type.

<3. Group Y>
Next, the self-refresh operation of the pixel circuits belonging to the group Y will be described for each type.

  Each type of pixel circuit in group Y has a configuration in which the control terminal of the transistor T4 is connected to the boost line BST and the selection line SEL is eliminated from the same type of pixel circuit in group X. Here, referring to the timing chart of each type of pixel circuit in group X, it can be seen that a high-level voltage is applied to the boost line BST at least between times t1 and t7. Therefore, in view of this, in each configuration of the group Y, it means that the transistor T4 is forcibly conducted over this period.

(First type)
As shown in FIG. 26, in the first type pixel circuit 2B of group X, the self-refresh operation is executed even when a high level voltage is applied to the selection line SEL over the self-refresh operation period. Therefore, it can be seen that the self-refresh operation can be performed for the first type pixel circuit 2b (FIG. 20) of the group Y by applying a voltage to each line other than the selection line SEL in the same manner as in FIG. A timing chart in this case is shown in FIG.

(Type 2)
In the pixel circuit 2c shown in FIG. 21, a voltage application state similar to that in FIG. 34 can be realized by making the applied voltage to the source line SL the same as the voltage supply line VSL shown in FIG. A timing chart in this case is shown in FIG.

(4th type)
The same voltage state as that of the first type pixel circuit (FIG. 20) is realized by applying the same voltage to the fourth type pixel circuit (FIG. 22) of the group Y as in the timing chart shown in FIG. I understand that I can do it. That is, the self-refresh operation can be realized by the same voltage application method as in FIG.

(5th type)
The same voltage state as that of the second type pixel circuit (FIG. 21) is realized by applying the same voltage to the fifth type pixel circuit (FIG. 23) of the group Y as in the timing chart shown in FIG. I understand that I can do it. That is, the self-refresh operation can be realized by the same voltage application method as in FIG.

<4. Another Example>
Hereinafter, other embodiments related to the self-refresh operation will be described together.

  <1> When the self-refresh operation is performed on the pixel circuits 2A of the group W, in FIGS. 24 to 25, in step # 4 in which a voltage of 0 V is supplied from the source line SL to the internal node N1 (time t4 to t5) ), 0 V, which is the same as that of the source line SL, is applied to the voltage supply line VSL.

  On the other hand, as shown in FIG. 36, a method of applying the first voltage state (5 V) to the voltage supply line VSL also in step # 4 can be theoretically assumed. In the case of this method, since the transistor T1 is non-conductive in the case L, this voltage is applied to the internal node N1 via the second switch circuit 23 even when 5V is applied to the voltage supply line VSL. There is nothing.

  On the other hand, in the case H, since the transistor T1 is turned on, the source line to which 0 V is applied from the voltage supply line VSL to which 5 V is applied through the internal node N1 from time t4 to t5. A current path toward SL is formed. As a result, the potential of the internal node N1 shows an intermediate value between 0V and 5V (see VN1 (H) at times t4 to t5 in FIG. 36).

  However, at time t5, the voltage applied to the gate line GL decreases, and the transistor T3 is turned off. As a result, in the case H, 5 V is applied from the voltage supply line VSL to the internal node N1 via the second switch circuit 23. This is refreshed to the first voltage state.

  That is, it is possible to refresh both cases H and L by such a method. However, as described above, since the current path from the voltage supply line SL to the source line SL is formed in the case H pixel circuit from time t4 to time t5, the voltage application shown in FIGS. Compared with the method, the amount of power consumption increases. From the viewpoint of suppressing power consumption, the voltage application method shown in FIGS. 24 to 25 is more preferable. This means that 0 V should be applied to the voltage supply line VSL only at least between times t4 and t5. In other words, the voltage applied to the voltage supply line VSL is reduced to 0 V simultaneously with the rise timing of the voltage applied to the gate line GL, and simultaneously with the timing when the voltage applied to the gate line GL is lowered to a low level. The applied voltage may be increased to 5V.

  As shown in FIGS. 24 to 25, while the voltage applied to the voltage supply line VSL is 0V, the potential of the node N1 (H) is also lowered to 0V, and then refreshed to 5V. Since the node N1 (H) is originally a node of a circuit written at a high level (first voltage state), flicker may occur if the period during which the node is lowered to 0 V is long. For this reason, it is preferable to shorten the period during which the node N1 (H) is lowered to 0V as much as possible. From this point of view, the time during which the node N1 (H) is reduced to 0V is reduced from time t4 to t5 by making the time from time t3 to t4 and the time from time t5 to t6 as short as possible or almost close to 0. A method of limiting in between is preferable. Thereby, the self-refresh operation can be executed while suppressing the occurrence of flicker.

  <2> Referring to the timing chart of another embodiment shown in FIG. 36, the applied voltage of the voltage supply line VSL is fixed to 5 V over the self-refresh operation period. Therefore, even when the voltage supply line VSL is also used as the auxiliary capacitance line CSL and the voltage applied to the auxiliary capacitance line CSL is fixed at 5 V, the voltage application state similar to that in FIG. 36 can be realized. That is, also in the group W, a type (third type) pixel circuit in which the voltage supply line VSL is also used as the auxiliary capacitance line CSL can be theoretically realized. However, as described above in the different embodiment <1>, the first to second type pixel circuits are more preferable in the group W in terms of suppressing power consumption.

  <3> In the above-described other embodiments of <1> and <2>, a current path from the voltage supply line VSL to the source line SL is formed in the case H when refreshing to the second voltage state. Talk about the case. Also in other pixel types, a voltage application method in which such a current path is formed can be adopted.

  For example, in the fourth type pixel circuit 2E (FIG. 13) of the group X, a method of applying the voltage (5V) in the first voltage state to the voltage supply line VSL during the self-refresh operation period is conceivable. Also, a pixel circuit 2H in which the transistor T4 is shared by the first switch circuit 22 and the second switch circuit 23 is assumed for the third type pixel circuit 2D of group X shown in FIG. 12 (see FIG. 37). A similar voltage state is realized. Further, in the group Y, the same voltage state is also realized when a configuration in which the voltage supply line VSL is also used as the auxiliary capacitance line CSL is assumed (the pixel circuit 2e in FIG. 38 and the pixel circuit 2h in FIG. 39).

[Third Embodiment]
In the third embodiment, the writing operation in the constant display mode will be described for each type with reference to the drawings.

  In the writing operation in the constant display mode, the pixel data for one frame is divided into display lines in the horizontal direction (row direction), and each pixel data for one display line is divided into the source line SL in each column for each horizontal period. A binary voltage corresponding to 1 is applied, that is, a high level voltage (5 V) or a low level voltage (0 V). Then, the selected row voltage 8V is applied to the gate line GL of the selected display line (selected row), and the first switch circuits 22 of all the pixel circuits 2 in the selected row are turned on, and the source of each column The voltage of the line SL is transferred to the internal node N1 of each pixel circuit 2 in the selected row.

  A non-selected row voltage of −5 V is applied to the gate lines GL other than the selected display line (non-selected row) in order to turn off the first switch circuits 22 of all the pixel circuits 2 in the selected row. . Note that the display control circuit 11 controls the voltage application timing of each signal line in the write operation described below. The individual voltage application is performed by the display control circuit 11, the counter electrode drive circuit 12, the source driver 13, and the gate. This is done by the driver 14.

<1. Group W>
First, the writing operation in the always-on display mode for the group W pixel circuit (FIG. 7) in which the second switch circuit 23 is composed only of the transistor T1 will be described.

  FIG. 40 shows a timing chart of a write operation using the first type pixel circuit 2A (FIG. 7). In FIG. 40, the voltage waveforms of two gate lines GL1, GL2, two source lines SL1, SL2, voltage supply line VSL, reference line REF, auxiliary capacitance line CSL, and boost line BST in one frame period are opposed to each other. The voltage waveform of the voltage Vcom is illustrated. Further, in FIG. 40, a fluctuation waveform of the potential VN1 of the internal node N1 of the two pixel circuits 2A is also displayed. One of the two pixel circuits 2A is a pixel circuit 2A (a) selected by the gate line GL1 and the source line SL1, and the other is a pixel circuit 2A (b) selected by the gate line GL1 and the source line SL2. They are distinguished from each other by adding (a) and (b) behind VN1 in the figure.

  One frame period is divided into horizontal periods corresponding to the number of gate lines GL, and gate lines GL1 to GLn selected in each horizontal period are assigned in order. FIG. 40 illustrates voltage changes of the two gate lines GL1 and GL2 in the first two horizontal periods. In the first horizontal period, the selected row voltage 8V is applied to the gate line GL1, and the unselected row voltage -5V is applied to the gate line GL2. In the second horizontal period, the selected row voltage 8V is applied to the gate line GL1. A non-selected row voltage of -5V is applied, and in the subsequent horizontal period, a non-selected row voltage of -5V is applied to both gate lines GL1, GL2.

  A voltage (5 V, 0 V) corresponding to the pixel data of the display line corresponding to each horizontal period is applied to the source line SL of each column. In FIG. 40, two source lines SL1 and SL2 are shown as representatives of each source line SL. In the example shown in FIG. 40, the voltage of the two source lines SL1 and SL2 in the first one horizontal period is set to 5V and 0V in order to explain the change of the internal node potential VN1.

  In the pixel circuit 2A, since the first switch circuit 22 is composed only of the transistor T3, the on / off control of only the transistor T3 is sufficient for the control of the conduction / non-conduction of the first switch circuit 22. In the pixel circuit 2A, the high level voltage needs to be applied to the voltage supply line VSL at the time of writing as described above in the description of the first embodiment.

  The applied voltage of the boost line BST is 0V. Further, the reference line REF is higher than the high level voltage (5 V) by a threshold voltage (about 2 V) or more in order to keep the transistor T2 in an on state regardless of the voltage state of the internal node N1 during one frame period. Apply 8V. As a result, the output node N2 and the internal node N1 are electrically connected, and the auxiliary capacitive element Cs connected to the internal node N1 can be used to hold the potential VN1 of the internal node, which contributes to stabilization. The auxiliary capacitance line CSL is fixed to a predetermined fixed voltage (for example, 0 V). The counter voltage Vcom is subjected to the above-described counter AC drive, but is fixed to 0 V or 5 V during one frame period. In FIG. 40, the counter voltage Vcom is fixed at 0V.

<2. Group X>
A writing operation of the pixel circuit of group X in which the second switch circuit 23 is configured by a series circuit of transistors T1 and T4 and the control terminal of the transistor T4 is connected to the selection line SEL will be described.

(First type)
FIG. 41 shows a timing diagram of a write operation using the first type pixel circuit 2B (FIGS. 8 to 10). Unlike the group W, the pixel circuit of the group X includes the transistor T4 in the second switch circuit 23. Since it is not necessary to turn on the second switch circuit 23 during the write operation, the transistor T4 may be turned off by applying a low level voltage to the selection line SEL. Here, it was set to -5V.

  In this case, since the second switch circuit 23 is turned off during the write operation, the voltage applied to the voltage supply line VSL can be set to 0 V unlike the group W. Since other points overlap with the explanation of the group W, they are omitted.

(Second to third type)
If the timing diagram of the write operation in the first type pixel circuit 2B shown in FIG. 41 is seen, a low level voltage is always applied to the selection line SEL over one frame period. That is, the second switch circuit 23 is always non-conductive.

  Accordingly, in the second type pixel circuit 2C in which one end of the second switch circuit 23 is connected to the source line SL and in the third type pixel circuit 2D connected to the auxiliary capacitance line CSL, each line other than the voltage supply line VSL is connected to each line. On the other hand, a write operation is possible by applying a voltage in the same manner as in the first type timing chart.

(4th type)
In the fourth type pixel circuit 2E shown in FIGS. 13 to 16, since the first switch circuit 22 is configured by a series circuit of the transistor T3 and the transistor T4, it is necessary to conduct not only the transistor T3 but also T4 at the time of writing. There is. In this respect, the sequence is different from the first to third types.

  FIG. 42 shows a timing chart of the write operation using the fifth type pixel circuit 2D. 42, items shown in FIG. 41 are common except that two selection lines SEL1 and SEL2 are shown.

  The voltage application timing and voltage amplitude of the gate lines GL (GL1, GL2) and the source lines SL (SL1, SL2) are exactly the same as those in FIG.

  In the pixel circuit 2E, the first switch circuit 22 is composed of a series circuit of the transistor T3 and the transistor T4. Therefore, when controlling the conduction / non-conduction of the first switch circuit 22, in addition to the on / off control of the transistor T3. Therefore, on / off control of the transistor T4 is required. Therefore, in this type, it is necessary not to control all the selection lines SEL at once, but to control them individually for each row, like the gate lines GL. That is, one selection line SEL is provided for each row, the same number as the gate lines GL1 to GLn, and the selection lines SEL are sequentially selected in the same manner as the gate lines GL1 to GLn.

  FIG. 42 illustrates voltage changes of the two selection lines SEL1 and SEL2 in the first two horizontal periods. In the first horizontal period, the selection voltage 8V is applied to the selection line SEL1, and the non-selection voltage -5V is applied to the selection line SEL2. In the second horizontal period, the selection voltage 8V is applied to the selection line SEL2. The non-selection voltage -5V is applied, and in the subsequent horizontal period, the non-selection voltage -5V is applied to both the selection lines SEL1 and SEL2.

  The voltage applied to the reference line REF, the auxiliary capacitance line CSL, the boost line BST, and the counter voltage Vcom are the same as the first type shown in FIG. In the non-selected row, when the first switch circuit 22 is turned off, the transistor T3 is completely turned off, so that the non-selection voltage of the selection line SEL for turning off the transistor T4 is , It may be 0V instead of -5V.

  In the case of this type of pixel circuit, it is desirable to apply 5 V to the voltage supply line VSL, as in the case of the group W shown in FIG. This is due to the following reason.

  When a low-level voltage is applied to the voltage supply line VSL under a state where it is written at a high level, the transistor T1 becomes conductive. In this case, it is assumed that during the write operation, the source line SL connected to one end of the first switch circuit 22 which is in the conductive state at the same time and the voltage supply line VSL connected to one end of the second switch circuit 23 are applied. If there is a difference in voltage, a current path is generated between the source line SL and the voltage supply line VSL, and the voltage of the node located in the middle fluctuates. As a result, the correct voltage corresponding to the write data is written to the internal node N1. It may not be possible.

  On the other hand, by applying 5V (first voltage state) to the voltage supply line VSL, the transistor T1 in the diode connection state is set in the reverse bias state (off state), so that the second switch circuit 23 in the selected row is turned on. A non-conducting state can be achieved. As a result, the voltage applied to the voltage supply line VSL does not affect the write voltage.

(5th type)
In the fifth type pixel circuit 2F shown in FIGS. 17 to 19 as well, in the same way as in the fourth type, the selection lines SEL are not collectively controlled, but individually for each row, like the gate lines GL. Need to control. That is, one selection line SEL is provided for each row, the same number as the gate lines GL1 to GLn, and the selection lines SEL are sequentially selected in the same manner as the gate lines GL1 to GLn.

  In the case of this type of configuration, since the second switch circuit 23 is connected to the source line SL together with the first switch circuit 22, the potential VN1 of the internal node varies even when the transistor T4 is turned on during writing. Because there is no, there is no need for special treatment. Therefore, the write operation can be executed by applying the same voltage as in FIG. 42 to each line other than the voltage supply line VSL.

<3. Group Y>
The write operation of the pixel circuit of group X in which the second switch circuit 23 is configured by a series circuit of transistors T1 and T4 and the control terminal of the transistor T4 is connected to the boost line BST will be described.

(First and second types)
If the timing diagram of the write operation in the first type pixel circuit 2B of group X shown in FIG. 41 is seen, a low level voltage is always applied to the selection line SEL over one frame period. That is, the second switch circuit 23 is always non-conductive, and the voltage applied to one end of the boost capacitor element Cbst does not change. This also applies to the second type.

  Therefore, for the first to second type pixel circuits 2b and 2c of the group Y, the write operation is performed by applying the same voltage as that of the group X of the same type to the other signal lines except the selection line SEL. Can be executed.

(4th to 5th type)
Referring to the timing chart of the write operation in the fourth type pixel circuit 2E of group X shown in FIG. 42, a high level voltage is applied to the selection line SEL to make the transistor T4 conductive in the selected row, and the non-selected row is applied. Applies a low level voltage to render transistor T4 non-conductive. Based on this, in the pixel circuit 2e (FIG. 22) of group Y, it is sufficient to apply a high level voltage to the boost line BST in the selected row and apply a low level voltage to the boost line BST in the non-selected row. I understand.

  Incidentally, in the case of the fourth type pixel circuit 2e (FIG. 22) of the group Y, when a high level voltage is applied to the boost line BST, the voltage applied to one end of the boost capacitor element Cbst also increases accordingly. However, during the write operation, a high level voltage (8 V) is applied to the reference line REF, and the transistor T2 is on. Since the node N1 having a large parasitic capacitance is electrically connected to the node N2, the potential of the output node N2 hardly increases. That is, even if a high level voltage is applied to the boost line BST, it is not necessary to consider the influence on the output node N2.

  Based on the above, when performing the write operation in the fourth to fifth type pixel circuits 2e and 2f of the group Y, in addition to applying the voltage to the boost line BST in the same manner as the selection line SEL, A voltage application similar to that of the similar type pixel circuit of group X may be performed.

[Fourth Embodiment]
In the fourth embodiment, the relationship between the self-refresh operation and the write operation in the constant display mode will be described.

  In the constant display mode, after the writing operation is performed on the image data for one frame, the display content obtained by the writing operation performed immediately before is maintained without performing the writing operation for a certain period.

  A voltage is applied to the pixel electrode 20 in each pixel through the source line SL by the writing operation. After that, the gate line GL becomes low level, and the transistor T4 is turned off. However, the potential of the pixel electrode 20 is held by the presence of charges accumulated in the pixel electrode 20 by the immediately preceding write operation. That is, the voltage Vlc is maintained between the pixel electrode 20 and the counter electrode 80. Thereby, even after the writing operation is completed, a state in which a voltage necessary for displaying image data is applied to both ends of the liquid crystal capacitor Clc is continued.

  When the potential of the counter electrode 80 is fixed, the liquid crystal voltage Vlc depends on the potential of the pixel electrode 20. This potential fluctuates with time as the leakage current of the transistor in the pixel circuit 2 is generated. For example, when the potential of the source line SL is lower than the potential of the internal node N1, a leakage current is generated from the internal node N1 toward the source line SL, and the potential VN1 of the internal node N1 decreases with time. On the contrary, when the potential of the source line SL is higher than the potential of the internal node N1, a leakage current from the source line SL toward the internal node N1 is generated, and the potential of the pixel electrode 20 increases with time. That is, when time passes without performing an external writing operation, the liquid crystal voltage Vlc gradually changes, and as a result, the display image also changes.

  In the normal display mode, the writing operation is executed for all the pixel circuits 2 every frame even for a still image. Therefore, the amount of charge accumulated in the pixel electrode 20 only needs to be maintained for one frame period. Since the amount of potential fluctuation of the pixel electrode 20 within one frame period is very small, the potential fluctuation during this period does not affect the displayed image data to a degree that can be visually confirmed. For this reason, in the normal display mode, the potential fluctuation of the pixel electrode 20 is not a serious problem.

  On the other hand, in the constant display mode, the writing operation is not executed every frame. Therefore, while the potential of the counter electrode 80 is fixed, it is necessary to hold the potential of the pixel electrode 20 (internal node potential VN1) for several frames in some cases. However, if the writing operation is not performed for several frame periods, the potential of the pixel electrode 20 varies intermittently due to the occurrence of the leakage current described above. As a result, the displayed image data may change to such an extent that it can be visually confirmed.

  In order to avoid such a phenomenon, in the constant display mode, the self-refresh operation and the write operation are executed in combination as shown in the flowchart of FIG. To reduce power consumption.

  First, the writing operation of pixel data for one frame in the constant display mode is executed as described above in the third embodiment (step # 11).

  After the write operation in step # 11, the self-refresh operation is executed in the manner described above in the second embodiment (step # 12).

  When a request for a new pixel data writing operation (data rewriting), an external refresh operation, or an external polarity inversion operation is received in a waiting period after the self-refresh operation is performed until the self-refresh operation is performed again (step # 13). YES), the process returns to step # 11 to execute the writing operation of new pixel data or previous pixel data. If the request is not received (NO in step # 13), the process returns to step # 12 to execute the self-refresh operation again. Thereby, the change of the display image by the influence of leak current can be suppressed.

  If the refresh operation is performed by the write operation without performing the self-refresh operation, the power consumption is expressed by the relational expression shown in the above formula 1, but if the self-refresh operation is repeated at the same refresh rate, all sources Since the line voltage is driven once, the variable m in Equation 1 is 1, and assuming VGA as the display resolution (number of pixels), m = 1920 and n = 480, so that it is about 1/1000. Reduction of power consumption is expected.

  In the present embodiment, the reason why the self-refresh operation and the external refresh operation or the external polarity inversion operation are used in combination is that even if the pixel circuit 2 was normally operating at first, the second switch circuit 23 is changed due to aging. Alternatively, a problem occurs in the control circuit 24, and the writing operation can be performed without any problem, but a case where a state where the self-refresh operation cannot be normally performed occurs in some of the pixel circuits 2. That is, depending on only the self-refresh operation, the display of some of the pixel circuits 2 deteriorates and is fixed, but the external polarity inversion operation is used together to prevent the display defect from being fixed. be able to.

[Fifth Embodiment]
In the fifth embodiment, the writing operation in the normal display mode will be described for each type with reference to the drawings.

  In the writing operation in the normal display mode, pixel data for one frame is divided into display lines in the horizontal direction (row direction), and each pixel data for one display line is divided into the source line SL in each column for each horizontal period. Are applied to the gate line GL of the selected display line (selected row), and the first switch of all the pixel circuits 2 in the selected row is applied. In this operation, the circuit 22 is turned on and the voltage of the source line SL in each column is transferred to the internal node N1 of each pixel circuit 2 in the selected row. A non-selected row voltage of −5 V is applied to the gate lines GL other than the selected display line (non-selected row) in order to turn off the first switch circuits 22 of all the pixel circuits 2 in the selected row. .

  The display control circuit 11 controls the voltage application timing of each signal line in the write operation described below. The voltage application is performed by the display control circuit 11, the counter electrode drive circuit 12, the source driver 13, and the gate driver 14. Is done by.

  FIG. 44 shows a timing diagram of a write operation using the pixel circuit 2A of the group W. 44, the voltage waveforms of the two gate lines GL1 and GL2, the two source lines SL1 and SL2, the selection line SEL, the reference line REF, the auxiliary capacitance line CSL, and the boost line BST in one frame period are opposed to each other. The voltage waveform of the voltage Vcom is illustrated.

  One frame period is divided into horizontal periods corresponding to the number of gate lines GL, and gate lines GL1 to GLn selected in each horizontal period are assigned in order. FIG. 44 illustrates voltage changes of the two gate lines GL1 and GL2 in the first two horizontal periods. In the first horizontal period, the selected row voltage 8V is applied to the gate line GL1, and the unselected row voltage -5V is applied to the gate line GL2. In the second horizontal period, the selected row voltage 8V is applied to the gate line GL2, and the gate line GL1. The unselected row voltage -5V is applied to each of the gate lines. In the horizontal period thereafter, the unselected row voltage -5V is applied to both gate lines GL1 and GL2.

  A multi-gradation analog voltage corresponding to the pixel data of the display line corresponding to each horizontal period is applied to the source line SL of each column. Note that in the normal display mode, multi-gradation analog voltages corresponding to the pixel data of the analog display line are applied, and the applied voltage is not uniquely specified. In FIG. 44, this is expressed by being shaded. . In FIG. 44, two source lines SL1, SL2 are shown as representatives of the source lines SL1, SL2,... SLm.

  Since the counter voltage Vcom changes every horizontal period (opposite AC drive), the analog voltage has a voltage value corresponding to the counter voltage Vcom in the same horizontal period. That is, the analog voltage applied to the source line SL is set so that the absolute value of the liquid crystal voltage Vlc given by Equation 2 does not change and only the polarity changes depending on whether the counter voltage Vcom is 5 V or 0 V.

  In addition, a voltage that always turns on the transistor T2 regardless of the voltage state of the internal node N1 is applied to the reference line REF for one frame period. This voltage value may be a voltage that is higher than the maximum value among the voltage values given from the source line SL as a multi-gradation analog voltage by at least the threshold voltage of the transistor T2. In FIG. 44, the maximum value is 5 V, the threshold voltage is 2 V, and 8 V larger than the sum of them is applied.

  Since the counter voltage Vcom is counter AC driven every horizontal period, the storage capacitor line CSL is driven to have the same voltage as the counter voltage Vcom. The pixel electrode 20 is capacitively coupled to the counter electrode 80 via the liquid crystal layer, and is also capacitively coupled to the auxiliary capacitance line CSL via the auxiliary capacitance element Cs. For this reason, when the voltage on the auxiliary capacitance line CSL side of the auxiliary capacitance element C2 is fixed, the change in the counter voltage Vcom is distributed between the auxiliary capacitance line CSL and the auxiliary capacitance element C2 and appears on the pixel electrode 20, and the non-selected row The liquid crystal voltage Vlc of the pixel circuit 2 varies. Accordingly, by driving all the auxiliary capacitance lines CSL to the same voltage as the counter voltage Vcom, the voltages of the counter electrode 80 and the pixel electrode 20 change in the same voltage direction, and the liquid crystal voltage Vlc of the pixel circuit 2 in the non-selected row. Fluctuations can be suppressed.

  Note that, as described in the third embodiment, the voltage applied to the voltage supply line VSL is set to 5 V for the same reason as that in the writing operation in the constant display mode.

  The writing operation in the normal display mode is different from the constant display mode only in that the voltage value written through the source line SL becomes an analog value. Therefore, the write operation for each type of pixel circuit of group X and each type of pixel circuit of group Y is also the same as that of the third embodiment except that an analog voltage corresponding to data is applied to the source line SL. Writing can be done in the same way as described. Details are omitted.

  In addition, in the writing operation in the normal display mode, as a method of inverting the polarity of each display line every horizontal period, a predetermined fixed voltage is applied to the counter electrode 80 as the counter voltage Vcom in addition to the above-described “counter AC drive”. There is a way to do it. According to this method, the voltage applied to the pixel electrode 20 alternates every horizontal period when it becomes a positive voltage and a negative voltage with reference to the counter voltage Vcom.

  In this case, the counter voltage Vcom is written by a method of directly writing the pixel voltage through the source line SL and a voltage in a voltage range centered on the counter voltage Vcom, and then by capacitive coupling using the auxiliary capacitance element Cs. There is also a method of adjusting the voltage so that either a positive voltage or a negative voltage is used as a reference. In this case, the auxiliary capacitance line CSL is not driven to the same voltage as the counter voltage Vcom but is individually pulse-driven in units of rows.

  In the present embodiment, the method of inverting the polarity of each display line every horizontal period in the writing operation in the normal display mode is adopted. This occurs when the polarity is inverted in units of one frame. This is to eliminate the inconvenience shown. As a method for solving such inconvenience, there are a method of polarity inversion driving for each column and a method of polarity inversion driving for each pixel at the same time in the row and column directions.

  Assume that a positive liquid crystal voltage Vlc is applied to all pixels in a certain frame F1, and a negative liquid crystal voltage Vlc is applied to all pixels in the next frame F2. Even when a voltage having the same absolute value is applied to the liquid crystal layer 75, a slight difference may occur in the light transmittance depending on the positive polarity or the negative polarity. When a high-quality still image is displayed, the slight difference may cause a minute change in the display mode between the frames F1 and F2. In addition, even when displaying a moving image, there is a possibility that a fine change may occur in the display mode in the display area that should have the same display content between frames. When displaying a high-quality still image or moving image, it is assumed that such a minute change can be visually recognized.

  Since the normal display mode is a mode for displaying such a high-quality still image or moving image, there is a possibility that the minute change as described above may be visually recognized. In order to avoid such a phenomenon, in this embodiment, the polarity is inverted for each display line in the same frame. Thereby, since the liquid crystal voltage Vlc having a different polarity between the display lines is applied even within the same frame, the influence on the display image data based on the polarity of the liquid crystal voltage Vlc can be suppressed.

[Another embodiment]
Hereinafter, another embodiment will be described.

  <1> For the pixel circuits belonging to the group X, a low level voltage may be applied to the reference line REF and the transistor T2 may be turned off during the writing operation in the normal display mode and the constant display mode. As a result, the internal node N1 and the output node N2 are electrically separated, so that the potential of the pixel electrode 20 is not affected by the voltage of the output node N2 before the writing operation. Thereby, the voltage of the pixel electrode 20 correctly reflects the voltage applied to the source line SL, and the image data can be displayed without error.

  However, as described above, the total parasitic capacitance of the node N1 is much larger than that of the node N2, and the potential of the initial state of the node N2 hardly affects the potential of the pixel electrode 20, so that the transistor T2 It is also preferable to always keep the on state.

  <2> In the above embodiment, the second switch circuit 23 and the control circuit 24 are provided for all the pixel circuits 2 configured on the active matrix substrate 10. On the other hand, when the active matrix substrate 10 is configured to include two types of pixel portions, that is, a transmissive pixel portion that performs transmissive liquid crystal display and a reflective pixel portion that performs reflective liquid crystal display, only the pixel circuit of the reflective pixel portion is provided. The second switch circuit 23 and the control circuit 24 may be provided, and the pixel circuit of the transmissive display unit may not include the second switch circuit 23 and the control circuit 24.

  In this case, an image is displayed by the transmissive pixel portion in the normal display mode, and an image is displayed by the reflective pixel portion in the constant display mode. With this configuration, the number of elements formed on the entire active matrix substrate 10 can be reduced.

  <3> In the above embodiment, each pixel circuit 2 includes the auxiliary capacitance element Cs. However, the pixel circuit 2 may include no auxiliary capacitance element Cs. However, in order to further stabilize the potential of the internal node N1 and to reliably stabilize the display image, it is preferable to include this auxiliary capacitance element Cs.

  <4> In the above embodiment, it is assumed that the display element unit 21 of each pixel circuit 2 includes only the unit liquid crystal display element Clc. However, as shown in FIG. 45, the internal node N1 and the pixel electrode 20 An analog amplifier Amp (voltage amplifier) may be provided between them. In FIG. 45, as an example, the auxiliary capacitor line CSL and the power supply line Vcc are input as power supply lines for the analog amplifier Amp.

  In this case, the voltage applied to the internal node N1 is amplified by the amplification factor η set by the analog amplifier Amp, and the amplified voltage is supplied to the pixel electrode 20. Therefore, the configuration can reflect a minute voltage change of the internal node N1 in the display image. In FIG. 45, the group X pixel circuits are illustrated as an example, but the pixel circuits of the groups W and Y can of course be realized.

  <5> In the above embodiment, assuming that 0V and 5V are the voltage values of the first and second voltage states of the internal node N1 and the counter voltage Vcom in the constant display mode, the voltage value applied to each signal line In response to this, -5V, 0V, 5V, 8V, and 10V are set. However, these voltage values can be appropriately changed according to the characteristics (threshold voltage, etc.) of the liquid crystal element and the transistor element to be used. .

  <6> In the above embodiment, the liquid crystal display device has been described as an example. However, the present invention is not limited to this, and has a capacitance corresponding to the pixel capacitance Cp for holding pixel data. The present invention can be applied to any display device that displays an image based on the voltage held in the capacitor.

  For example, in the case of an organic EL (Electroluminescenece) display device that displays an image by holding a voltage corresponding to pixel data in a capacitor corresponding to a pixel capacitor, the present invention can be applied particularly to a self-refresh operation. FIG. 46 is a circuit diagram showing an example of a pixel circuit of such an organic EL display device. In this pixel circuit, a voltage held in the auxiliary capacitor Cs as pixel data is applied to the gate terminal of the driving transistor Tdv constituted by the TFT, and a current corresponding to the voltage is supplied to the light emitting element via the driving transistor Tdv. Flows to OLED. Therefore, the auxiliary capacitor Cs corresponds to the pixel capacitor Cp in the above embodiments. In FIG. 46, the group X pixel circuits are illustrated as an example, but the pixel circuits of the groups W and Y can also be realized.

1: Liquid crystal display device 2: Pixel circuit 2A, 2B, 2B, 2C, 2D, 2E, 2F, 2H: Pixel circuit 2a, 2b, 2b, 2c, 2e, 2e, 2f, 2h: Pixel circuit 10: Active matrix substrate 11: Display control circuit 12: Counter electrode drive circuit 13: Source driver 14: Gate driver 20: Pixel electrode 21: Display element unit 22: First switch circuit 23: Second switch circuit 24: Control circuit 31: Delay circuit 74: Sealing material
75: Liquid crystal layer 80: Counter electrode 81: Counter substrate Amp: Analog amplifier BST: Boost line Cbst: Boost capacitor element CD: Delay capacitor element Clc: Liquid crystal display element CML: Counter electrode line CSL: Auxiliary capacitor line Cs: Auxiliary capacitor Element Ct: Timing signal DA: Digital image signal Dv: Data signal GL (GL1, GL2,..., GLn): Gate line Gtc: Scanning side timing control signal N1: Internal node N2: Output node OLED: Light emitting element REF: Reference Lines Sc1, Sc2,..., Scm: Source signal SEL: Selection line SL (SL1, SL2,..., SLm): Source line Stc: Data side timing control signal T1, T2, T3, T4, T5: Transistor TD1, TD2: delay transistor Tdv: Dynamic transistor Vcom: counter voltage Vlc: liquid crystal voltages VN1: internal node potential VN2: the output node potential VSL: voltage supply line

Claims (9)

A display device having a pixel circuit group in which a plurality of pixel circuits are arranged,
The pixel circuit includes:
A display element unit including a unit display element;
An internal node that forms part of the display element unit and holds a voltage of pixel data applied to the display element unit;
A first switch circuit for transferring a voltage of the pixel data supplied from a data signal line to the internal node via at least a predetermined switch element;
A second switch circuit for transferring a voltage supplied to a predetermined voltage supply line to the internal node without passing through the predetermined switch element;
A control circuit for holding a predetermined voltage corresponding to the voltage of the pixel data held by the internal node at one end of the first capacitor element and controlling conduction / non-conduction of the second switch circuit,
Of the first and second transistor elements having a first terminal, a second terminal, and a control terminal for controlling conduction between the first and second terminals, the second switch circuit includes the first transistor element. Each of the control circuits has the second transistor element,
The control circuit includes a series circuit of the second transistor element and the first capacitor element,
One end of the first switch circuit is connected to the data signal line,
One end of the second switch circuit is connected to the voltage supply line,
The other ends of the first and second switch circuits and the first terminal of the second transistor element are connected to the internal node,
A control terminal of the first transistor element, a second terminal of the second transistor element, and one end of the first capacitor element are connected to each other to form an output node of the control circuit;
A control terminal of the second transistor element is connected to the first control line;
The other end of the first capacitive element is connected to a second control line;
The predetermined switch element is a third transistor element having a first terminal, a second terminal, and a control terminal for controlling conduction between the first and second terminals, and the control terminal is connected to a scanning signal line. Is a configuration to
A data signal line driving circuit for driving the data signal line separately, a control line driving circuit for driving the first control line, the second control line, and the voltage supply line separately, and scanning for driving the scanning signal line It has a signal line drive circuit,
For a plurality of the pixel circuits, the data signal line drive circuit, the control line drive circuit, during a self-refresh operation that operates the second switch circuit and the control circuit to simultaneously compensate for voltage fluctuations of the internal node, And the scanning signal line driving circuit is configured to control the operation according to a predetermined sequence,
The predetermined sequence is:
The scanning signal line driving circuit applies a first scanning voltage to the scanning signal lines connected to all the pixel circuits included in the pixel circuit group, thereby bringing the third transistor element into a non-conductive state. When,
When the voltage state of the binary pixel data held by the internal node is the first voltage state with respect to the first control line, the control line driving circuit causes the first capacitor element to be driven by the second transistor element. A second step of applying a first control voltage that cuts off a current from one end of the transistor to the internal node and makes the second transistor element conductive when in a second voltage state;
After execution of the first and second steps, the control line driving circuit applies the first boost voltage to the second control line, whereby the first capacitive element is connected to one end of the first capacitive element. When the voltage of the internal node is in the first voltage state, the first transistor element is turned on without being suppressed when the voltage of the internal node is in the first voltage state. A third step of bringing the first transistor element into a non-conducting state when the voltage is in the second voltage state;
After the third step, the control line driving circuit changes the voltage applied to the first control line to the second control voltage, so that the voltage state of the internal node is the first voltage state or the second voltage. A fourth step of interrupting a current from one end of the first capacitive element toward the internal node by the second transistor element regardless of a state;
After the fourth step, the scanning signal line driving circuit applies a second scanning voltage to the scanning signal lines connected to all of the pixel circuits included in the pixel circuit group to thereby apply the third transistor element. And the data line drive control circuit applies a voltage of the pixel data in the second voltage state to the data signal line;
After the fifth step, the scanning signal line driving circuit applies the first scanning voltage to the scanning signal lines connected to all the pixel circuits included in the pixel circuit group to thereby apply the third transistor. The element is turned off, and the control line driving circuit applies the voltage of the pixel data in the first voltage state to all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. And a sixth step. The second switch circuit is configured by a series circuit of a fourth transistor element having a control terminal connected to a third control line and the first transistor element,
The control line driving circuit is configured to drive the third control line in addition to the first and second control lines,
The sixth step of the predetermined sequence includes:
All of the control line driving circuits connected to the plurality of pixel circuits to be subjected to the self-refresh operation in a state where the fourth transistor element is turned on by applying a predetermined voltage to the third control line. The display device according to claim 1, wherein the display device is configured to apply a voltage of the pixel data in the first voltage state to the voltage supply line. The data signal line is also used as the voltage supply line,
The sixth step of the predetermined sequence includes:
Instead of the control line driving circuit, the data line driving circuit applies the first voltage to the data signal lines that also serve as all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. The display device according to claim 2, which is an operation of applying a voltage of the pixel data in a state. The pixel circuit further includes a second capacitor element having one end connected to the internal node and the other end connected to a fourth control line,
The fourth control line is also configured as the voltage supply line,
In the predetermined sequence, the first voltage state is applied to all the fourth control lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation by the control line driving circuit over the first to sixth steps. The display device according to claim 2, further comprising an operation of applying a voltage of the pixel data. In the pixel circuit, the first switch circuit controls a series circuit of the fourth transistor element and the third transistor element in the second switch circuit, or controls the fourth transistor element in the second switch circuit. A fifth transistor having a control terminal connected to the terminal and the third transistor element;
The predetermined sequence has an operation in which at least in the fifth step and the sixth step, the control line driving circuit applies a predetermined voltage to the third control line to make the fourth transistor element conductive. The display device according to claim 2, wherein the display device is a display device.
  2. The display according to claim 1, wherein the second switch circuit includes a series circuit of a fourth transistor element having a control terminal connected to the second control line and the first transistor element. apparatus. The data signal line is also used as the voltage supply line,
The sixth step in the predetermined sequence includes:
Instead of the control line driving circuit, the data line driving circuit applies the first voltage to the data signal lines that also serve as all the voltage supply lines connected to the plurality of pixel circuits that are the targets of the self-refresh operation. The display device according to claim 6, which is an operation of applying a voltage of the pixel data in a state. In the pixel circuit, the first switch circuit controls a series circuit of the fourth transistor element and the third transistor element in the second switch circuit, or controls the fourth transistor element in the second switch circuit. The display device according to claim 6, wherein the display device is configured by a series circuit of a fifth transistor having a control terminal connected to a terminal and the third transistor element.
The predetermined sequence is:
After the sixth step, the control line driving circuit changes the voltage applied to the first control line to a third control voltage, so that the voltage state of the internal node is the first voltage state or the second voltage. 8. The seventh step according to claim 1, further comprising: a seventh step of conducting the second transistor element regardless of a state to make the internal node and the output node have the same potential. The display device described in 1.

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